Girl’s sister is actually her mom

I’m looking for a movie I saw part of in a hotel. I saw it in 2007/8 but from the the lighting/coloring I would assume it was made in the 90s. In the movie, a young girl is being raised by her biological grandmother because her mother had her really young. The girl thinks her mother is her (obviously much older) sister. I don’t remember much else except for one sort of gross detail. The girl gets mad at her sister/mother for something so she leaves some kind of condiment on her bedsheets so the mother/grandmother will think she’s having sex. I know this is not much to go on but it’s been driving me crazy for years. Thanks!