You sound like such a practical person about the entire thing!  It is difficult to give guidance in contract cases without being able to read the contract to make sure that it is "legal" for lack of a better word.  But assuming it is, if she agreed to the terms of the contract and signed it then it is binding.  Even if this contract were subject to state laws on 3 day rights of rescission, we are way past the 3 days.  What really worries me is bad press, so to speak.  Your reputation in the wedding business means a lot.  It may be a good idea to negotiate the matter with her rather than have mud slung at you.  You were lucky enough to re-book.  But remember: you would be within your rights to keep the money based upon the contract terms stated here.  Good luck.