If your baby's buttocks are very irritated and causing her pain, it is important to seek medical advice. You can consider using a zinc-based ointment to help treat the irritation. It is also recommended to allow some time for the skin to breathe without a diaper, as this can aid in healing. If there is no improvement or if her condition worsens, do not hesitate to consult a healthcare professional. Wishing your baby a speedy recovery.