Since she is such a phobic I would start off by telling her that it is not contagious and she can't catch it from you or anyone else. That may be all that needs to be said. Brain was right on about people such as her. Although, some people like her will freak out and start thinking they have it. Sad but it does happen.

You can always explain that your nervous system is not communicating properly and your wires get short circuited.

Let us know how it goes.