I was 24 when I had Heidi in 1993, two years after her brother, Jacob, was born. I adored being pregnant. I carried easily and recovered without any problems. Heidi and I were always close. We shared a love of music, Disney and a positive outlook on life. By adulthood she was my best friend, and lived 30 minutes from my house in California.

She dreamed of being a mother. So, in 2016, seeing her and her husband, John, struggle to conceive was heartbreaking. They tried for four years until finally, in 2020, it happened. Hearing she was pregnant with twins, I dissolved into happy tears.

Our joy didn’t last. At 10 weeks Heidi lost one of the babies, and at 24 weeks their little boy, whom they named Malakai, also died. Watching Heidi’s grief was awful. I felt helpless.

Then a few weeks later Heidi told me: “Mom, the doctors think that IVF and surrogacy is the best next step.” Finally, here was something I could do. “Please let me speak to your doctor about being your surrogate,” I said. “What safer place for your baby than their grandmother’s womb?”

I could see both hope and caution in Heidi’s eyes. I was 52, she said. The last thing she wanted to do was to put me in danger. But I was fit, healthy and also retired, with all the time in the world. I could tell Heidi was worried that I was only offering out of obligation. I reassured her that that couldn’t be further from the truth.

A week later I spoke to Heidi’s doctor. The cutoff age for surrogates is usually 35 where we live, so I thought he would equivocate. Instead, he was positive. “If everything checks out,” he said, “there shouldn’t be a problem.”

It was only then that I told my husband, Ray, who was immediately on board. Still, we kept our plan to close family only. We didn’t want the extra pressure if it didn’t work out.

After tests and counselling, we were given the green light. When the doctor finally implanted an embryo in my uterus in July 2021, I wasn’t watching the screen. I was looking at Heidi’s face as it lit up with joy.

Nine days later, I had a positive pregnancy test. We called our partners to tell them, and we all cried with happiness.

I hadn’t been pregnant for 28 years, but it all came flooding back. It felt natural and joyful to see my body change. I even celebrated the tiredness and morning sickness as signs that things were going well.

As my pregnancy became obvious, I didn’t go out much, because I didn’t want to hear people say: “Kristi, you’re pregnant!” I wanted Heidi to have the congratulations and excitement. Ray enjoyed watching my transformation. He loved joking with people. “My wife is pregnant – but it’s not mine,” he’d say gleefully to strangers. He’d then say, “She’s carrying our grandbaby!”

Not everyone was supportive. Some thought I was taking the experience away from Heidi; others thought I was having a baby with John. “I had nothing to do with conceiving this child, I’m just a safe place for it to grow,” I’d explain.

People find it hard to believe, but I never felt like a mother in waiting when I was pregnant – my bond with this child was nothing like it had been with Heidi and Jacob. I planned for the baby to go immediately to Heidi for skin-to-skin contact after the birth.

I felt a wave of happiness when my granddaughter, Ekko, was born, in March 2022, at 6lb 4oz (2.8kg). I had experienced the post-birth hormone rush twice before, and thought I might be weepy and need to hold her. In fact, seeing Ekko in Heidi’s arms, I felt only joy. Ekko was exactly where she was meant to be.

Ekko was taken to a neonatal intensive care unit for observation, so it was seven days before I held her for the first time. Having her in my arms was amazing – but I felt like a proud grandmother, not a mum. And two years later, as my gorgeous, cheeky granddaughter calls me Gigi and runs into my arms, it’s the same.

I look back on the experience with wonder and gratitude. I’ll be forever thankful that I was able to help bring Ekko into this world, and to make Heidi a mum at last. Even now, Heidi says that she can never thank me enough for what I did. But I don’t need any thanks.

• As told to Kate Graham

Do you have an experience to share? Email experience@theguardian.com