L.M.
a few things ask the teacher to insist that dd stop playing and use the bathroom.
Is there any chance she loves the new outfits you pack for her or that the school gives her to wear. PIck something ugly and horrible and maybe that iwll lose some appeal.
the teachers are going to look at this as accidents and not get mad or anything, but you really should talk to them and see what might be motivating her to do this. have the teacher track when it is happening, like when they play outside and she's seen her change of clothes in her bookbag or cubbie. ask if there is some spececial attention she gets like the director gets her her clothes or she gets out of a certain activity by doing this like circle time.
good luck this too shall pass and then you can bring it up on prom night.