Health, weight, teenager (my sibling, need advice)

My sister is going in to her sophomore year in HS and a new school at that. She's trying to lose weight but it's just not working and her acne keeps going in and out worse than before and she just isn't motivated anymore. She just bought a bikini and that was the 1st brave thing she's done but then she has this sweater fetish that I know she uses as a comfort shield. Then her body has its own odor that she refuses to get under control (like I said no longer motivated) and she gets really mad if me or my mom say something about it. What do we do, any advice would help?