My daughter Sidonie was 10 when she put a message in a bottle and threw it into the sea. We were visiting friends in Long Island, New York, at the time and she always disappeared with their children immediately, engrossed in some project or other. I knew what they were doing, but didn't think much about it.

Eight years later, in 2010, my world was torn apart. Sidonie went on a picnic with her school while in Switzerland; the students were in an area where there weren't many barriers and she fell 1,500ft down a cliff. She was 18. I was a single mother and she was my only child. I felt everything was lost and for many months it was very hard to continue.

I surrounded myself with photos of Sidonie. I was so grateful that she had been very creative: she left hundreds of pictures that she had painted for me to treasure and I lined the walls with them. But I found it very hard to reconcile myself to her death. It is human nature always to look for signs; clues to help me understand what had happened. I would often speak to the parents of a boy who had died in the same accident as Sidonie and it helped to be in contact with someone who was connected with her, however loosely.

Then, in December last year, I got a message on my answerphone: "Be excellent to yourself, dude," said a friendly voice, along with his name and number, asking me to call back when I could. I instantly realised it was someone reading from Sidonie's message in a bottle, launched 12 years earlier. I couldn't believe it: a funny, light-hearted message from my daughter. I sobbed and sobbed, but this time they were tears of joy.

That phone message brought her memory back to me in fresh and vibrant colours. I could hear her saying the quote from one of her favourite films, Bill And Ted's Excellent Adventure. It summed up her positive, carefree approach to life. I felt that I needed to hold the bottle in my hands as soon as possible and rang the number left on my answerphone.

I got through to Brian, who explained that he worked for the parks department in the small town of Patchogue, two miles down the coast from where we had stayed in Long Island all those years ago. Sidonie had written our phone number on the message in a bottle but no name, so when I told him that I was her mother and that she was dead, his initial amusement turned to shock and sadness.

Yet I felt hugely relieved that I still had the same phone number 12 years on. Many people in New York no longer have landlines, but I've kept mine since 1977. Brian told me that he had found the bottle while he was clearing the beach of debris from hurricane Sandy, which devastated the entire eastern seaboard of the US last year.

I had felt its effects in New York when the storm surge flooded the streets and caused power cuts. It felt miraculous, magical, that this same storm that had caused so much damage should bring something so wonderful back to me. I went to Patchogue two days later and Brian was there to meet me off the train.

He gave me the bottle – a small green glass ginger-ale bottle – and when I unfurled the message, there was Sidonie's childish handwriting. It felt like discovering buried treasure. It also felt as if she was telling me everything was all right. It was a beautiful message for a mother to get.

I was taken to the beach where it was found and when I saw the tonnes of rubbish and the bulldozers that were clearing it, I was dumbfounded that Sidonie's bottle was retrieved unbroken among it.

In July, a plaque was unveiled in Patchogue with a picture of Sidonie on it: it was wonderful and very touching that the people in this small town seemed to care so much. I loved it that they all spoke about Sidonie as if they had known her. It was heartening to hear.

Although Sidonie's message in a bottle is very precious, I am planning to donate it to the Museum of the City of New York, because I want everyone to be able to enjoy it. Sidonie always left a lasting impression wherever she went, and I want that to continue.

• Do you have an experience to share? If so, email experience@theguardian.com