"Flattering" means to hide features that don't look good and/or highlight the ones that do. In her case, nothing looks good (she'll probably say she has big tits or ass, nope they look like shit) so there is nothing to show off or draw attention to, and pretty much every part of her is hideous. The goal for a stylist then would be to hide her whole body, hence the shapeless colorless pieces that just drape over her. It's really the best they can do. She doesn't even have a waist to make some sort of shape out of her.