@Patty:
I'm a bit disturbed about the 'matted crud' that you say she always has around her vulva. That seems quite unusual to me - a bitch normally keeps herself very clean - there should be no reason for it and I think it could be that she has some internal infection. Has she had this ever since you had her?
Please do try and get her to the vets as soon as possible and in the meantime use whatever has been suggested to stop the itching.
Patty, have to disagree. Sayblee and MOST my dogs have kept self clean. Arwen and Cara and one of my Rotties consider that my job. The Rottie only got crud if she gained weight, making her vaginal area "fluffier" and kept moisture. But Arwen is actually on the thin side now and just the way it folds I have to use a baby wipe and clean at least weekly, ditto for Cara.
Benedryl will help the itching, but I have to agree with the rest… vet asap unless you can put something on her to stop her from continually licking (like an eliz collar). Some cortizone ointment on the area might help, but you'll need to keep her off it for an hour and then wipe off to prevent her from ingesting it.