I remember reading this book as a child (probably 10-12 years ago, making me around 12 to 14 years old) when I started learning the English language (native Dutch speaker) by reading books. So I'm sure it wasn't too complicated a book, and most likely in the children section of the library. I'm not too confident in the following details, but in my memory it was probably about 70 pages, and had an orange tinted hardcover showing a (flying?) dragon.
The book started out with a girl sitting on a boat (Either a big sailboat or yacht I think) while on vacation with her family. While on the boat she was reading (possibly writing) a (fantasy) book. I think her personality was a recluse without many friends. Then something makes her lose balance and fall into the water.
Falling into the water transports her into a dream world/other dimension (possibly the one she was reading/writing about). Where I think she finds herself in a maze in a desert like area. Obviously lost she starts wandering around, meeting dangers and running from it until she comes across a dragon she befriends. I do not recall any other humans being in this world. Just animals and mythical beasts.
Together with the dragon they explore the world, and she learns how to make friends. the details of what kind of things they do have escaped me.
At the end of the book she gets rescued from the water while keeping the memories of the other world she was in.
I think it was a single book and not part of a series. I don't know the origins of the story but it felt like a pretty new book when I read it. The language was definitely in English, but obtained in a Dutch (the Netherlands) library. It wasn't for a school assignment or anything, so it doesn't necessarily have to be "school children friendly", as I think it included fighting as well.