Avoid pointing out that clothes being worn are dirty, which puts the person on the defensive and sets up an argument she doesn’t understand.
Ask yourself if you’re bothered by the repetition of the outfit or by actual dirt or odor (A couple of generations ago, people didn’t change clothes every day).
Pare down the closet to fewer options. Stock solids in favorite colors instead of patterns.
Buy an identical replacement for favorite outfits (same color, style) so you can wash one while the other is being worn.
Remove soiled clothing from the room at night once the person is sound asleep. They’ll forget about it the next morning if there’s something else handy to put on.