I'm going to be brutally honest.
Those outfits are "in". Big sweaters and leggings. Hell, they have leg warmers again. Welcome back to the 80s. I'm 41. Guess what I wore for Christmas eve church and family gathering after? Big sweater, black leggings, leg warmers and fuzzy boots. My niece in HS wore pretty much the same outfit. That's the style. So what if you thought it was too cold for it? It's the style. Exactly how long would she have been standing around out in the cold. If she wants to be cold for a little bit, let her.
Also. She's bipolar. I'm bipolar. I have a very nasty and violent temper. Don't push me. Just walk away. You kept at her over her clothing? She's 18 and an adult whether you like it or not. You see her about ready to explode you don't push her more. It's like teasing a caged tiger and then letting it out. Is it acceptable behavior? Of course not. Do you think she could have controlled herself? I doubt it in the state of mind she was in. The fight was ridiculous, imo. Good lord, you should have seen what I wore when I was 18.