Stop caring about her so much. You love her too much. It's normal and natural for us men to feel this way, it happens to me too. The only way to succeed in this, is to stop caring.
If you try to tell her to stop, she will feel that you are too controlling, or she might be sweet and listen to you - but then she will do it when you aren't looking.
If you stay quiet, it will eat you up inside and ruin your happiness/confidence. You may start to worry about guys hitting on her, and why is she looking for this attention, etc..
You can't allow her to feel like she has to "hide things" from you, so you don't get upset. This opens the door to her having a secret, second "outlet" where she can do the stuff she likes when you aren't around. Like wearing the stuff she likes to wear. And that might even lead to more secrets behind your back. And it makes you look like a *****.
Just get it into your brain that she, at any point in time, can completely destroy you emotionally and stick a knife in your back with any guy she wants, even your best friends.
So, stop caring about stuff like this. Have your fun, screw her brains out, love her the right amount, spend time with her like any fun loving normal couple, but stop sweating her. If the way she dresses one day leads to her ****ing some other guy, shrug your shoulders, throw her out of your life, and move on.
Stop caring.