When you're with your own peer group, that YOU like what you're wearing is very important. But when you're going to be with your mom's peer group, it's very important to wear something that doesn't make your mom uncomfortable in front of her group. How you dress reflects on her.
She's not asking you to wear something you hate, something that makes you feel embarrassed and ashamed She's asking you to NOT wear something SHE hates, something that makes HER feel embarrassed and ashamed. You should be thankful, not resentful. A lot of parents would just tell you "We're having company. I laid out clothes for you" and not allow you any choice at all.
You have lots of other clothes to choose from. Go select an ensemble that is acceptable to your mom. And for pete's sake, that "If she doesn't like the clothes I choose, it means she doesn't like ME" is bull biscuit. Lose that babyish whine.