Of course it is not proper to let her keep the dirty clothes where your baby also stay there !! If I were u....... if I have 2 toilets, I will let her keep in the guest toilet, if I have 1 only, I will ask her to wash every night....
I also give her a bucket & a face container, and ask her to wash her clothes at any spare times (when nothing to do) she wants. Usually she hand washes her clothes every tuesday & friday.