im looking for a teen book about rich families where the two girl teenage cousins hate each other as one is bad and one is good?
I have done some research with no luck in finding a book which meets the criteria you have stated.
A few more details might help;
Time Frame: when did the story take place.
Setting: Do you remember a town, a country, a state.
Character names: Can you think of any of the character names.
Even details which seem insignificant may aide in the search for the book's title.