The more you discourage her from wearing those clothes, the more she will want to wear them, I'll bet. One thing a teenager never listens to is the mother's perspective. What you need to do is find someone else's perspective. When my mom tells me that I look stupid, I will wear it. When a friend or another family member tells me I look stupid, it hurts my feelings and I will never wear it again. Does she have an aunt or someone that you can urge to comment to your daughter about her clothing? Just get her to say "Those clothes look like they were made for a child." I wouldn't say that the clothes look too tight on her, or too small, or that she is too heavy for them -- that will just make her feel fat. It's better to say that the clothes look like they are designed for someone much younger. Another thing teens don't like to hear -- anything that has to do with them being childish in any way.