If it happens occasionally when you're not looking, it's ok. You can't watch her every second of the day. Cookie, and Kaiser as well, both chase their tails a lot too. Cookie doesn't do it as much as she used to. Not only is it dangerous physically, but it can become psychologically damaging as well. I saw a dog on America's Funniest Home Video's last night laying on a couch, eating a bone, and the whole time the poor dog was snapping and snarling at his back foot, he thought it was going to take his bone. And you could hear the children in the backround laughing at the dog. This is not funny. You should never ever promote this kind of behavior, the dog is resourse gaurding against his foot and I've also seen it done with there tails too. This is very stressful for the dog as it is constantly gaurding things from it's tail or feet.
So I would say keep doing what you're doing, if you catch her in the act, re-direct her behavior to something better for her, but if you don't always catch her, no harm done. Most dogs don't depelop this obsession with resourse gaurding against themselves, but it can happen.
