She's very young, and lots of black and tan dogs will have black on their paws when they are puppies, especially those who will be blanket patterned as adults. My 6 year old female also had black on her toes and back legs when she was a puppy. As she grew up the black receded a bit up her legs, and the markings on her toes and heels disappeared. There is a chance that one or both parents carry the bi-color gene (which is recessive to black and tan, but dominant to black) and a litter from two black and tans could throw a bi-color, but in this case she doesn't look bi-color, at least not to me.