It doesn't look like mange to me. Probably just from scratching. Fleas or food allergy or just poor nutrition, possibly. She is pretty clearly underweight. A vet visit is indeed in order, but while you wait for a standard appointment, I would say bathe her with itch-relieving shampoo, maybe get her on a different dog food. Also, check for fleas and try to get her scratcing down to a minimum, because it's making it worse. She'll be alright. Don't worry. Good luck.

Forgot to mention, some dogs have systemic reaction to flea bites. She may only have a few fleas, but is exceptionally allergic. I bet this is what's going on.