Hello there.....generally to assess correctly why the lady would do this you would have to know the full context of the situation when she is doing it. Is it when something particular is being said?...is the situation shes in uncomfortable for her? etc....but to be on your toes when seated is usually a gesture that displays that some anxiety is present. Being on the toes whilst seated normally indicates that she is getting ready to leave...or her emotions are saying that she wants to remove herself from the situation at that time as she is feeling uncomfortable... hope this helps !:)