What do you do about a friend who dresses inappropriately and the clothes just aren't flattering?

So I love my best friend to death... but she has gotten a little... bigger. She is not fat at all, but she is not as thin as she used to be. But she still wears the clothes that she wore when she was tiny.. and it doesn't help that her chest it HUGE like triple D's, and she has a little.. gut, but she always wear short shorts and tight tank tops with her boobs and stomach out.. I took her with me yesterday to an office type setting, to pick something up and she wore these little short shorts and a tank with all her chest out and it was just not... OK. I am not gonna lie I have gone up a pant size too and I am not totally comfortable with my weight gain but... I wear appropriate clothing.. like jeans and a top with a flairy top... or shorts that fit and a flairy top... I just don't like to go out with her when she looks all... you know inappropriate, but I don't want her to get pissed at me if I tell her you know?
What do you do about a friend who dresses inappropriately and the clothes just aren't flattering?
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