A.D.
Just have her change her own wet underwear, have her bring the wet ones to the laundry area herself, have her go and get and put on her own dry ones before she can resume whatever activity she was doing. Don't run around and try to do it for her, and don't make it easier by running around and cleaning up after her while she sits and waits for you to do all the running around for her. Tell her that when she is ready to pull down her underwear, she will be able to get back to her fun as fast as everyone else who uses the toilet. Let her decide on her own when she is tired of this chore. Good luck!