She's nibbling. It is a pit bull trait I guess you could call it. My male dog is a bit OCD with his nibbling, he does the cats, the pillows, the sofa, the bed.........anything he can get his teeth on. He does it also to calm himself down when he gets really excited. My female does it to but not to the extent he does.
There's a fine line between genius and insanity. I have erased this line.