First of all, have you done anything to relieve her diaper rash. Is she allergic to something you are using? Does she have to stay for a long time with an unchanged diaper on? You can use some cornstarch as dusting powder on her bottom to cool down the irritation, but that is not a substitute for medical care when needed or diaper changes.

Dear Lord Jesus, you loved the children in a very special way, I pray for this wee little one who is suffering, give her parent wisdom and help in solving this and heal the child. In your Name, Amen.