Hi, Welcome to Hcm, Poor girl must be having teroble pain. Its although hard to diagnose such lesions without having a look at it. I however get a feeling it could be a fungal infection especially because its spreading. I suggest you to keep that area as dry as possible that means not to let any wetness like sweat or urine get accumulated. But if she has pain due to friction can apply soothening agent like coconut oil or moisturizer. For a proper diagnosis, better she is seen by a dermatologist. Wish your child a good health. Take care.