Diaper rash

Fl

My friends baby girl has had a rash all over the downstairs area from having bad diarrhea. She said the diarrhea is getting better but the rash is not. It's red all over. She said it's been like that for over three weeks. Her doctor even prescribed cream, but it didn't help. Shes lets the baby stay naked for long periods of times, tried almost every cream, and uses wash cloths instead of wipes. Any advice?