Teething 8 month old baby girl?

my baby is teething and everytime she pees she screams because it burns and she poops 20 times a dal. but she keeps gettin a bad rash from pooping so much, i change her after n make sure shes clean down there ,I also let her air dry for awhile. then i use diaper rash cream. it goes away for awhile then comes right back so what can i do to prevent her gettin this painful rash. what foods should she not eat or foods to help? things to avoid? thanks for ur help