My Sadie (13months) has started doing this also, but I think in her case it is allergy related. We just switched her food from Iams LBP, to Eagle Holistic Chicken & Rice LB Adult. We switched her slowly over about 12 days, but 5 days into the switch-over, she started licking, knawing at her paws. Sometimes front legs, sometimes back, not canstantly but often enough. We are now on the Eagle pack 100% but it has only been a few days now. It's hard to say if it is getting worse or not. It's been about the same I guess. I have a bad feeling tis food isn't going to work out, but I'm giving it time.
I can't be of much help besides giving my version of a similar situation. I suspect the rice in Sadie's new diet. Are you feeding a form of rice/grains in your home cooked? Perhaps you should try eliminating one ingridient at a time, in the hope of seeing a change in her licking. That is, if it is food related to start with.
Keep us posted!