So you probably figured out that the answer to this scenario is:
a) WRONG – bad form. don’t sink to her level, what’s the point.
b) WRONG – you could sue her or at least try but it will cost you so much more emotionally and financially then it’s worth
c) CORRECT: just let it go. Do not sink to her level and give her the satisfaction of knowing that she’s getting to you. However, if it does go on too long or gets particularly harassing then definitely contact your attorney. A simple letter may do the trick. If not, then a modification may be necessary to include “no harassment” in your orders. A mediator may be able to solve this as well for less cost.
d) Yes and No: Definitely move on – wouldn’t that be great if it were that easy, but when you do, there will be no need to rub it in her face – she will already know.