Keep a diaper off of her as much as humanly possible. I know it sounds tough, but you can use the potty pads, etc. Get as much air, cream free, as you can.
Her little hiney being able to breathe is the best thing. Give her a break between diapers and be sure she is good and air dried after each bath and change.
My daughter developed an actual allergy to disposables so nothing I put on her made any difference. I switched to cloth diapers and she was without a diaper more than she had one on.
When my second baby came, I was afraid of a repeat so I did the same thing.
He had a happy little hiney.
Use warm wash cloths as opposed to baby wipes. They can sting. Rinse your babies hiney as opposed to rubbing.
I wish you the best. Tushy rashes are the worst.