Who is she making these accusations to? If she's only saying it to you, there isn't much you can do about it. If she's telling this to others, that could form the basis for a slander lawsuit. But you have to ask yourself whether this woman is mentally confused or not. If she is simply "off," try to ignore her. But if she has all her faculties and people might take her seriously, you should consult a Washington attorney about legal action.
A roundup of the best tips and legal advice.