My daughter was a her dads family this past weekend an she came back with a dog bite on her butt now its got a rash from the bite down her legs did the dog bite cause the rash

No need to post twice. Here is my answer from your first post:

You must take her to the doctor and have the bite treated, diagnosed. All dog bites must be reported, which the doctor is required to do by law. Shame on him for not doing this immediately. If it was his dog, he probably didn't want it impounded.

Any break in the skin followed by a spreading rash must be treated IMMEDIATELY. I and others on this site have ended up in the hospital from cellulitis.