Would you tell your best friend something painful?

One of my best friends is going back to university soon and I'm wondering if I should give her some painful lifestyle advice. Since the new Barbie movie she has a habit of dressing in a single colour (usually pink or some soft colour).

Obviously this is a big fashion mistake but I don't know if I can tell her. For one thing, she seems improved compared to when she came home from university last year (back then, because of the way she dressed and acted, I thought she had converted to feminism/Atheism because she was acting sullen and dressed gothic/garish). Also, she is really fat. She used to be lithe like me but she likes cake too much and now she is a big girl.

Maybe the reason she dresses in block colours is an attempt to distract people from her weight. So would I be mean too bring it up?