Here are the things I have learned for treating rashes that you might want to try for a few days (be consistent for a few days to give it a chance to heal):
1. never use creamy diaper rash ointment of any kind on bum with open sores. these are designed to use on healthy skin as a protectant for over-night, etc.
2. after each poopy diaper, wash with water and rags (I rip up old t-shirts) instead of wet wipes (they have chemicals in them that can irritate damaged skin). Or you can rinse your wet wipes out first.
3. when possible, give her a bath (2 inches of water is fine) after each poopy diaper, let her play in there a little while (you can also add baking soda or oatmeal to the water; which are soothing for the skin).
4. when possible, let her play with a naked bum after the bath for a while (such as in the kitchen or outside?) to air dry.
5. before putting a diaper back on, while the bottom is nice and clean, you can use your blow dryer on her bum for a minute or two (hold it about a foot away and move it constantly). it will be warm and totally dry.
6. then smother the skin with a skin protectant like Vaseline to form a protective seal from future wetness and dirtiness until the next diaper change. I also like Bag Balm or Lanolin, though I hear some babies may be sensitive to lanolin.
7. Additionally, you will want to watch her diet while it heals. Especially, do not give her any apple or orange juice, sugary foods, etc. Bland foods such as the BRAT diet are helpful. Avoid other foods that might be causing her problems in the first place - such as suspected sensitivities or allergies.