contractor becomes victim of socialpath customer

i seem to have an issue with a customer of mine, after entering into a contract to resurface a set of exterior damaged concrete stairs,the job was started and completed in good faith as per the contract agreement. i have been paid for the job as agreed, and at that time the customer indicated that they were satisfied with the job. thru the duration of the job the customer (a lady) kept indicating how much she needs a man. i had absolutly no response to her comments. now 4 days after the job was completed and contract complety fulfilled, this customer has phoned my wife to tell her that the job was complete "s**t" and now has to find someone else to completly redo it and when my wife asked what was the issue with it, the client replied the same thing and refused to be specific when asked. keep in mind that i have done over 300 of these paticular jobs with complete sucess and not one unhappy customer, and know through expertise that there is absoluty nothing wrong with the job.
now after not returning my calls to see what the problem was she finally phones back to tell me that there is a water issue in her house (that was there previously and shows old water stains and damage over time and has nothing to do with what the contract that we agreed to.) now using an unrelated issue with her house she is annoucing publicly that the job i did is no good.
i have asked her out of good faith to let me come and look at the problem to see if it was the work that i preformed that caused this. (which i know it is not,other cause for water issue, not stairs) she refuses to give me the opper. to see if we can rectify the issue. but continues to complain, phone, harass. and publicly attacking me and my business. keep in mind that there is alot of untrustworthy contractors out there, and i do not concider myself as one of them. i take a lot of pride in my work and i will do anything resonable to keep my customers satisfied.
there are some people that no matter what u do u cant please them

now what options do i have , can i add something in my contract that would prevent them from publicly badmouthing myself and my business without cause?
this is a cut and paste from a section of my contract:

SECTION SIX
POSSESSION
Client shall not have possession, occupancy, build\construct on top, or use of the structure until such time as all payments or other obligations required to them as set forth in this agreement have been fully paid or performed by them. If possession or build\construct on top of or use of structure is taken by client before the above obligations are met, without the written consent of contractor, it shall be considered as acceptance of the structure, by the client, as complete and satisfactory.

now again what options do i have , can i add something in my contract that would prevent them from publicly badmouthing myself and my business without cause?

thanx