She-dog is an old southern expression used to infer a particular woman is like a female dog - and will "do it" with practically any male that comes along. (i.e., a slut).
Usage: I don't know how John Mike can trust any of those young-uns are his, that wife of his ain't nuthin' but an old she-dog.
Bobert: "Damn! Did you see Tara tonight?"
Jimothy: "Hell yeah, dogg. She'd give a dog a bone. Giggidy giggidy giggidy!"
Bobert: "Speaking of giving dogs bones, last night I came home real drunk, and my dog...um, yeah..."
Jimothy: "Hey, at least it wasn't a sheep this time."
Bobert: "Amen, brother."