Since there's not much information given, it's really hard to say. It might be a story that has significance only to Rachel and the person saying 'this is for Rachel'. Maybe it's a memory they share, or a special anecdote.
The significance could be related to some sort of inside joke or personal history between the speaker and Rachel. 'You big fat story' might be a term they use to describe a story that's been going around, perhaps one that Rachel is involved in. It could also be a way of getting Rachel's attention before telling her this story, which could be something important, funny, or embarrassing depending on the situation.
Well, it could be a rather rude or teasing statement. Maybe 'this' is something like a joke or a made - up tale directed at Rachel, and 'you big fat story' might be a way of saying the story is exaggerated or untrue. But without more context, it's hard to be sure.
Since I don't know the exact story, Rachel could be anyone. She could be a fictional character created for a novel, a real - life person that the storyteller knows personally, or just a name used in a parable.
Rachel Trapani could be a local figure in a particular town or city. Maybe she is known for her volunteer work and the 'Secret Story' could be about the real impact she has made through her selfless deeds, which are not widely known. It's also possible that she is an artist or a writer and the story is related to her creative process that she has kept private.
I'm afraid I don't have enough information to tell Rachel's back story. It could involve things like her education. For example, if she went to a special school or had a particular teacher who influenced her a great deal. It might also include her relationships with friends or early romantic interests.