Apologies for how vague this is, and please don't take any one detail as true 🤣
I think the writer wrote other teen books. maybe something like point horror as that's why it was bought for me
It's about a blonde girl in maybe california who was maybe picked up when hitch hiking. She was that she's immortal. maybe that she's god. I seem to remember she doesn't sleep. Her name was maybe Sadie.
She dies die at the end of the book. maybe poisoned by a friend.....
I read it early/mid 90s and I think it was aimed at teens.
That's all I've got but it's driving me insane!