You could probably find a local attorney willing to write 'her' a letter or maybe even get a restraining order, but do you really think that would stop her??
Personally, I think that you are fighting a losing battle. Unless 'she' violates a criminal law (trespassing, stalking, etc.) allowing you to let others (police, DA's, courts) fight the battle for you. Otherwise you will spend far more time, money and mental worry chasing this person... and that is exactly what she wants you to do!!!! You are letting her win by letting her get to you!!
One of the great things about this country is its freedom for all. However, this freedom applies to the stupid and the inane also. Those are the ones who complain and cry about every perceived injustice or wrong-doing, even when it is not true. They still have the right to complain... to a point. Regretfully, it sounds like your 'complainer' has not reached that point with the authorities.
Eventually, assuming that every investigation she files is false and after the investigation has run its course, she will become known as a crackpot or constant complainer to the authorities and they will quit responding to her complaints.
Currently, you are letting her 'get to you', just as she wants to. You need to try to calm down and try to dismiss her tactics as what they are. Do not lower yourself to her level and go about your life, believe it or not, this problem will go away by itself.
I suggest that you contact the local police or sheriff and the local prosecutor and let them know of your problems with this person.
I am sorry that I cannot offer any better specific legal advice.... but it appears that this person is within there rights to lodge civil complaints.