You might look into these things:
1)Change diaper brands. Many contain some toxic stuff that's not skin-friendly.
2)Change wetwipes to a chemical-free brand. They are hard to find, but you can find them--or use a washrag with water and a natural oil--like coconut or olive.
3) If you're not dealing with diapers, you might look into candida. Google it and see symptoms. She could have others, and it will explain how to treat at home. No big deal at all.
4) Could be food or other environmental allergies.
Hope this helps!
Blessings,
H.