A goody-two-shoes blonde girl gets suspended (expelled?) from her school and visits her rich dad to ask if she can move in with him, but her wretched mother intervenes, so the blonde chick runs to her poor, black sheep, rocker sister with dark hair (because edgy) who works at a diner and is dating a musician. Blonde chick asks about her sister and some cute guy leads her to her locker in the back and blonde chick puts on sister’s clothes. Blondie, sister, and possibly others go to a party that goes wrong in which someone punches someone in the face. Blondie is oddly exhilarated and calls her mom and says she won’t be coming back.
…and then my roommate changed the channel so I don’t know what happens after. I think there’s a significant cassette in the movie somewhere.
Sounds like an episode of the tv show Gossip Girl. What you described sounds like the flashback lily van der woodsen has about how she ended up in the city. The episode (season 2 episode 24) is titled valley girls. Brittany snow and Krysten Ritter played the flashback characters.
Lol this is definitely gossip girl!