Have you taken her to a Vet to see if she's micro-chipped? She definitely has some German Shepherd and I'm guessing some Labrador too.
Go to petfinder.com and put in German Shepherd and you'll be able to view pages upon pages of German Shepherds and German Shepherd mixes. Actually being able to view other German Shepherd / Lab mixes might answer your question.
At first I thought part collie but the fur would be a lot longer and the muzzle more narrow. She's got the Shepherd ears no doubt but also the thickness of a Labrador Retriever.
By
01/14/2011
How long have you had her? Did you post signs with her picture around your neighborhood? Or placing a "found" ad in the local paper? If it was around New Year's Eve, she might have been freaked out by the fireworks or gun shots and got out of her backyard. She does look like a black German Shepherd. She also looks well taken care of and healthy (like she belongs to someone), so I'm doubting she is a stray. I would be heartbroken if I lost her and had no way of knowing who had her. =(