The following is excerpted from SISTERS FIRST: Stories From Our Wild and Wonderful Life. Join Jenna and Barbara for their Sisters First Tour in Birmingham, Alabama, this weekend. Tickets are available here.

By Jenna Bush Hager and Barbara Pierce Bush
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Barbara Bush with dog Millie 1989
Credit: Diana Walker/Getty Images

At ninety-two, Barbara Bush still writes letters. When my Ganny is cross, or when she is pleased, for that matter, she can't help but tell you, often in print. Her most recent letter to me arrived typed, its geometric letters practically jumping off the stark white page. From the first sentence, I knew she was angry.

That summer we had visited my grandparents in Maine and I'd organized a family tennis tournament. The teams were open to anyone, and as the organizer, hoping for a dramatic run to the finals, I picked the local tennis pro to be my partner. Sure enough, we prevailed over the other teams of cousins, uncles, and my aunt Doro. The stage was set for the deciding match against my dear cousin Wendy and her dad, Craig. A dozen family members and a few family friends came out to watch, waiting for some good or at least some entertaining tennis.

I put on a show. After missing a shot, I dropped down to the clay court to display my athleticism: doing first a plank and then a push-up. When I hit a particularly impressive shot, I did the worm—a body-shaking dance move where I shimmied along the ground—and received lots of cheers. After my partner and I won a game, I lifted my skirt to the audience and shook my huge tennis underpants.

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The person egging me on the most? My father. He cheered, "That's my girl!" He triggered a chorus of audience laughter, until I was running around the court, dancing a made-up jig and yelling: "Not today!" My partner and I lost the match, but I felt like I had won: In the bright summer sunlight, I had made some of the people I love most laugh.

Within a few weeks, Maine was long forgotten, the memories faded like the tans on our shoulders. I was back in New York, my mind occupied with the demands of work and children. I stood at my kitchen counter opening mail. Among the flyers and bills, I saw an envelope with my grandmother's familiar, loopy cursive. In it was a typed note addressed to both my dad and me. Like a lawyer building her case, Ganny recited my every unsportsmanlike infraction, from lifting my skirt to the cheers I had chosen to yell in the heat of the moment. And what was worse, in her eyes, was that I had done it all in front of my mom, my daughters, family guests, and most of all, Gampy, who had been raised with the highest standards of sportsmanship. She pointed out that Gampy's own mother, who was an avid athlete, a gracious (not to mention great!) tennis player, and a self-effacing woman, would have despised a display like mine. Ganny was deeply disappointed with me because of my behavior, and angry that my dad had encouraged it.

And that is my grandmother: exacting and determined to protect the ones she loves. My audacity had embarrassed Ganny; she thought her husband deserved a less juvenile display. I'm in my thirties, but my grandmother's words and reprimands can still sting, making me tear up and sniffle like a child. She had added a handwritten postscript: Throw this letter away. Don't mention this again! I dutifully tore up the pages as she'd ordered, but the thought that I had disappointed my precious grandfather was too much to bear.

There have been many other Ganny letters over the years, full of love, sometimes disdain, and always protective to the core. She is a woman of high standards but also fierce loyalty. If she believes you are in the right, she will defend you with- out reservation.

In the spring of 2001, Ganny had herself received a critical letter in the mail. Barbara and I had just been caught for underage drinking. In the note, a friend of my mom's pleaded with my grandmother to intervene and do something about our wild ways. My grandmother read the letter, and then furiously and impulsively penned one back, stating that her granddaughters were doing just fine, that we studied hard and we wanted to do good. She ended with her own zinger: If this woman were a true friend, she should support my mother and mind her own damn business. The Enforcer was doing what she does best: Enforcing! Protecting!

Jenna Bush Wishes a Happy 92nd Birthday to 'The Enforcer' With an Amazing Throwback Photo
Credit: @jennabhager

People stop me all the time—in airports, grocery stores, on the sidewalk—to tell me how much they adore my grandmother. One woman recently came up to me as I was boarding a flight and said, "I always dreamed of having a grandmother like yours! She seems like the type of woman who bakes amazing cookies." I laughed. I can honestly say that I have never tasted a cookie made by my grandmother. Or a cake, or a pie. I cannot remember Barbara Bush ever baking anything.

Is it her appearance—her neat sweater sets accessorized with pearls; or that stiffly styled, signature white hair—that makes people think of my grandmother as a domestic maven, a throwback to an earlier, far more deferential time? My Ganny—I can assure you—is a thoroughly modern woman. She has always been blunt. As first lady, she was vocal about things that could have made her unpopular. She came out as pro-choice, having an opinion different from her husband's, the person she adores most in the world. In 1989, two months after she became first lady, she toured Grandma's House, a care center for infants and small children with AIDS. There, at a time when many people were still terrified of the disease, she purposely held a baby, kissed a toddler, and hugged a grown woman, all diagnosed with HIV/AIDS, trying to break the deep stigma associated with the disease.

In private and in public, she speaks her mind, sometimes the very first thought that comes into it. During the 1984 presidential campaign, Ganny was asked to describe the Democratic vice presidential candidate, Geraldine Ferraro, and she replied that the word she would use "rhymes with rich." (Gampy and Gerry later became friends.) Twenty-four years later, she said of Republican vice presidential candidate Sarah Palin, "I sat next to her once, thought she was beautiful, and I think she's very happy in Alaska. And I hope she'll stay there."

She's also more than willing to say what she thinks within her own family. On one visit when my dad put his feet up on her coffee table, she told him, "I don't care if you are the president of the United States, take your feet off my coffee table." And my dad did. When Jon Meacham, Gampy's biographer, earnestly asked her on the back porch at Walker's Point if she had ever anticipated her son George becoming president, her answer was to laugh until she had tears in her eyes, and then answer with a resounding "No." If one of us says something smart, her favorite reply is, "Well, that's using your head for something other than a hat rack!"

Her love of animals is the stuff of family legend. She particularly loves her latest dog, Mini, who has bitten almost everyone in the family. So great is her loyalty to her four-legged companion that if someone tries to pet Mini and Mini bites, she will almost always defend Mini.

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But Ganny also has a very tender side. For years she has enjoyed needlepointing, making Christmas stockings for the entire family. Now she is making a stocking reserve, so that all the great-grandchildren, including any who might be born after she passes away, will have a Ganny stocking to hang for Santa. She has even made a plan to have someone else personalize them if she is no longer able.

Ganny, who married at nineteen, is an explorer. When my grandfather graduated from college they packed up their new baby, George, and drove their red Studebaker from Connecticut to West Texas, where they rented a duplex. The house at least had an indoor bathroom—most of the houses on the block had outhouses—but they had to share it with the residents on the other side of the house, a mother and a daughter who made their living as prostitutes. It must have been quite an experience for Ganny, who had grown up under the huge old oaks in Rye, New York, and was married in a white satin dress with eight bridesmaids. In the next few years, she would move with her husband to Bakersfield, California, and then back to West Texas, to Midland, where the surrounding towns had names like Notrees, meaning there wasn't even one tree poking up from the ground.

When my grandmother was in her sixties, she decided she would take her granddaughters, when they reached sixteen, on their own adventure. The two of them would travel to anywhere in the world they wanted. When our turn came, together, of course, since we were twins, Barbara and I chose Italy. We had never been to Europe, and we dreamed of star- filled nights and dining on pasta in piazzas. The three of us did stroll through museums, ruins, and cathedrals, and rode in a gondola, but in Venice, Ganny also took us to the famous Harry's Bar, announced that it was cocktail hour, and proceeded to buy us our first martini. With each sip, we felt closer to adulthood.

I didn't quite realize it then, but Ganny had met Gampy, the love of her life, when she was that same age, sixteen. By the age of twenty-eight, Ganny had already lost her mother in a car accident, given birth to three children, and buried one of them, Robin, who died of leukemia when she was only three. When I was twenty-eight, I was barely a newlywed. Today, my Ganny remembers not the sorrow, but the wonderful feeling of her darling daughter's "fat little arms around my neck." After Robin died, my grandfather wrote to his own mother that he liked "to think of Robin as though she were a part, a living part, of our vital and energetic and wonderful family of men and Bar. Bar and I wonder how long this will go on. We hope we will feel this genuine closeness when we are 83 and 82." And they still do, at ninety-three and ninety-two.

But there was a time when the sadness almost broke my grandmother, until she heard my then seven-year-old dad solemnly telling his friends he had to go inside because he needed to play with his mom. After that, she insisted every- one get out and live life, herself included. All those summers in the water, sand, and garden in Maine are as much a legacy of that determination as they are of her love of the outdoors.

I'm not sure if Ganny was tough before or if she became tough because of her early married life, living far from her family and far from everything she knew, grieving alone in dry, dusty West Texas. When at night I tuck in my blond, blue-eyed daughters—girls my dad says look like Robin once did— I cannot imagine how my grandmother found the strength to pass her own daughter's empty bed. But by the time I got to know her, Ganny's strength was so powerful it had truly become a force, a life force for those of us who know her.

For years, one of her favorite places to be has been in her garden at Walker's Point, planting, weeding, and pruning. I think of her like my childhood picture-book character, Miss Rumphius, who planted fields of lupine to make the world a more beautiful place. Today, Ganny, who is unsteady on her legs, rides around on a scooter, inspecting the landscaping, looking for places that need to be thinned or cleaned out, spots to add new plantings, all to ensure that Walker's Point will be even more beautiful after she is gone.

At night when we all gather for dinner, she still sits, as she always has, close to her husband. When someone says something particularly funny, she will laugh uproariously. Then she will look over at Gampy, who does not hear as well as she does, and will quickly add, "Say it again; say it again, please, so that Gampy can hear it too."

When I look in the mirror now, I see bits of my mother's features and recognize the sound of her Texas twang. But a lot of times when I speak, it's my grandmother, my strong, impulsively hilarious grandmother, whose voice I hear.

Excerpted from the SISTERS FIRST: Stories From Our Wild and Wonderful Life. Copyright © 2017 by Jenna Bush Hager and Barbara Pierce Bush. Reprinted with permission of Grand Central Publishing. All rights reserved.