Sounds to me like this is totally abnormal for her; she just went into maternal mode. And yeah, maybe she knows she's not his mother, but maybe she feels he needs one, and her instincts come into play. That is scary. . .
I agree, put her away next grooming session; hopefully as he grows her instincts will chill out. Good luck, sorry this happened, keep the bite really clean -- don't want an infection on top of everything else.
