Absolutely don't agree with you on this. If you say this is a group paid shoot, then I may agree that you have no control over what she's wearing. If she is one of your friends, then the more you should control her outfit. Have a discussion with her, use your charm to sweet-talk her to wear the best clothes you think she's suitable for. Even if this is a free of charge session, you have the say. Explain to her you are doing justice to her to make her look perfect in front of the camera.
As a photographer, you call the shots. You're the king. As a model, she do what you direct her to do. If she's a pro, then you discuss with her what you want to achieve, and work to a consensus. If she's not, then you decide for her!