Those of you who are having this problem are making sure your sims aren't wearing their work outfits at the time, right? I haven't encountered any dresser related problems myself; I only mention this because it's a very easy thing to overlook. I'm not sure why you can't plan other outfits while dressed for work, but the game says no.
now that i think about it, i tried when she came home from work
it can be it... when it worked she was actually in night clothes the day after
maybe that's because you can't change the work outfit