for Ten Rules for Living with My Sister by Ann M. Martin
Pearl's older sister Lexie is in eighth grade and has a boyfriend. Pearl's only boyfriend is the family's crabby cat, Bitey. Lexie is popular. Pearl is not, mostly because of the embarrassing Three Bad Things that happened in school and which no one has forgotten. Everything Pearl does seems to drive Lexie crazy. On top of that, their grandfather is moving into their family's apartment and taking over Pearl's room. How will these sisters share without driving one another crazy?
Pearl is good at making lists of rules, but sometimes, life doesn't play by the rules!