
She's not particularly unusual, simply developing a bad habit ("bad" as in *annoying*, not as "in horrendously dangerous world dominating behaviour") - distract her, :)
I wouldn't stand up as VS would suggest because as I see it (and probably the dog too :D ) you're only offering her a bigger area to grip (sort of "invitational" if you get my drift).
Distract if you think she's about to/likely to do it, brush her off if your timings slightly out

and say "ah, ah" at the same time, then distract and reward when she stops - be consistent, observant and "non-invitational" and you should overcome this quirky trait ;)
HTH, Teri