I know where you're coming from and I agree with Catherine C.
There's a difference between dressing for self expression (mismatched socks which is a current trend) and not knowing what looks good on you.
I believe dressing to flatter your body shape is a skill! They even have a show called "What Not to Wear," and while the American version borders on mean, the British version was very informative.
I work with my daughter to help her learn what looks good on her. We shop together, and while I never criticize her body, I will help her choose clothing that looks good on her. She's getting to the point where she can see what looks good and what doesn't. For example, she wanted a long dress because that's what was in the stores. She looks terrible in long dresses! Now, if she was insisting on getting one, I wouldn't stand in her way, but I did have her try a few on and she liked the "feel" of them. Then I told her for fun we would try on some shorter dresses. She immediately saw the difference in how she looked (and I didn't have to say anything). She chose a shorter dress on her own.
There was one instance where she wanted one of those short, drapy sweater things. The one she liked was soft, but I thought it looked ridiculous on her. However, she begged for it so we got it in purple.
She wore it to cheer, and one of her friends looked at her and said "WHAT are you wearing? You look like a bunch of grapes!" Now, it was one of her good friends and her friend didn't say it in a snotty or mean way. And she DID resemble the big bunch of Fruit of the Loom grapes!
My daughter wasn't upset or crying about it, but I did notice she shoved the sweater in the back of her closet and she never wore it again. Later on I allowed her to cut it up to make American Girl bedding!
If something looks terrible on your daughter, it's worth gently saying something. It's a hard road we navigate as parents; knowing when to step in or back off. I know I would want to know if I looked terrible.
As a note, I do have my daughter help ME pick out clothing. I want her to know that all women can have trouble finding what looks good on them, that it's okay for her to say something to me if it looks bad, and that we just keep looking.
Good luck!