I think she is doing it as a bored thing, tends to be when we are having stories or she is in teh car but I woudl like to stop it now before it moves on from the 2 fingers she is concentrating on.
I have cut her nails but she still tries ot bite them so that hasn't really worked. She also sucks her thumb, which I don't mind, so I don't want nasty tasting things if I can help it.