My daughter is teething and she has bad nappy rash. Is there anything good to use on the rash?

Yes. Typical diaper rashes respond to diaper cremes like desitin, (zinc oxide diaper cream) balmex, triple paste, dr flanders, calendula, etc. If it lasts more than three days with no improvement then it may be yeasty and using creams like tinactin, micatin, or a paste made out of probiotics can help.