No idea where to put this at all

My 4 yr old dd just came running out of the shower screaming cause she put soap in her fanny and its burning her.

(before any one asks y wasnt i watching her, i had dinner on, she was only going in to get poop off her foot)

any way, we have rinsed it out, but its still stinging her, shes walking round with her legs spread atm, not sure what to do next, im assuming the burning will fade?