R.P.
My daughter had a diaper rash due to having to wear hip braces she had stool in her diaper at all times from three weeks until 5 month old when she was able to only wear the brace at night. At about 4.5 months old my cousins wife told me about triple paste. The desitin, extra strength desitin, a&d, butt paste none of that helped. The only thing that worked was the triple paste. Its a tad expensive but worked wonders for her. I found travel tubes only at walmart but a big tube at target.
Also have you changed her diaper brand. My daughter can only use pampers baby dry or luvs. Those two are the same diaper just different front patterns. Both made by P&G.
Good luck!