You don't need to spend too much time on simple makeup. I just apply eyeshadow and eyeliner, and tie my hair back. It takes less than 5 minutes. Clothes other than sweats can be comfortable too.. I used to wear the same sweats everyday, I hated shopping like it was a chore, but I enjoy shopping casually now.

She was probably not realizing it's offensive to you. She thinks it could be a fun thing for the two of you to spend time together, and just wants to help. Don't take it personally, tell her that you will ask her when you actually want her help, I guess.