Assuming she asks to go outside (when she doesn't go in her corner), what about training her to ring a bell when she has to go? If the bell (accompanied by using the outdoor toilet) means huge praise or lots of treats, it might encourage her to want to go out more.
Yeast could definitely contribute to the problem, but if she did this in your basement, and stopped when you blocked off the area, it's unlikely. I would think...
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