If you want to be really crafty do this:
Explain to her that baggy clothing is simply the fashion of the day. Sure the clothing doesn't fit, but fashion hardly ever is about function.
Make sure to have previously found old photo albums of hers, and ascertained what fashion she was into as a youth.
Then point out that she did things in her youth which didn't make perfect 'sense' but that is simply part of self expression as we grow up. Likely if she is in say her 40s she was probably a teenager in the 80s where they wore rediculous neon, tight pants and notorious big hair 'poofs'
Extremely inefficient for walking through doors or wearing hats in the winter.
Find something about her that when she was a kid was purely fashion. As soon as you simply take the fashion argument to the plate, but approach it with intelligent self-awareness vs. teenage anger nobody can shake a stick at you. Every adult can remember what it was like to think about fashion when they were younger... even if they don't anymore when they're older.
Besides... fashion is a massive industry. Hell its bigger than skiing, so you could even tell her that you're doubling down and trying to think about fashion at the same time as skiing and school... just to keep your future options open.
She'll be re-ordering the 2x shit in no time.
We are newschoolers. Expect us.