Are you sure it's a foot problem? Knee and hip problems are common in many dog breeds. She should get her hips checked out to rule that out.
My old neighbor's AB/Pit cross had bad hips and he put her on glucosamine, which helped her immensely. She stopped limping within a couple weeks of starting treatment. You really have to stick with it and make it a part of her diet permanently. Talk to your vet about the dosage for a tiny dog like that.