Yesterday, a friend asked, "How do I tell a co-worker to step it up, style wise?" First thought? You don't. Next thought? If it's affecting her job, you say something - nicely. In some jobs, in fact in most jobs (at least in New York, the only city I've worked in as an adult), what you wear, and whether you're showered, made up, put together etc. will affect your performance. Mostly because it'll affect your confidence, but also because it affects how everyone else - the people you have to work with - will treat you. (This is obvious.)
But if you're not someone's boss, you don't want to sound like a Cornell Pi Phi, and you'd rather not quote Emily Blunt's "hideous skirt convention" line, what's the protocol? Have you had this dilemma? Because if it were me, I'd probably just suggest a joint shopping trip, "Hey! I need some new clothes, looks like you do, too!" or, "Remember that skirt you wore last week? It'd look really great with the jacket you have on today," but realistically, I'd never say anything of the sort. So, can you help her?