Without knowing more about the situation (and seeing the rash itself), it can be difficult to speculate, as there are a number of potential causes. However, one possibility is that all the moisture led to a candidal (yeast) rash, that will likely respond to topical medications. I suggest your friend take the child to a pediatrician for an evaluation. In the meantime, using a topical zinc oxide cream will not hurt, and if they are comfortable with it, than spreading a small amount of clotrimazole ointment on the area might help as well. Again, I stress, this is only based on conjecture. Only a doctor (or someone with a lot of child rearing experience) can accurately diagnose the rash.