Does she noly do it when she's getting ready to shed ?
I know several of mine do this same thing during shed week, and I've come to the conclusion that it IS uncomfortable, perhaps tender to the touch ?
The ones who do something similar when not in shed I call ticklish. They don't really jump, but they will twitch their bodies away if I run a gentle finger down their sides. They will even twitch away ahead of my finger, in anticipation of "being tickled" as I call it. They don't seem to mind if I do that every now and then, it's kind of a game we play.
Gale