I agree with Rohag and Lynn - get a camcorder. They are cheap now and also have a built in recorder - when she sees you with this she is most likely to back off and leave you alone. If not you can send the recording to the medical board. They can take the digital card and put into any computer now days, and watch and listen to her crazy rants.
My simpathys are with you - I'm so lucky to have such wonderful neighbors all around me - in fact, peole want to move into our neighborhood and no one wants to move out.
Best of luch to you Sunflower!!