Where do I file to revoke my power of attorney if she lives in another state?

Review your power of attorney and the state law where executed to comply with revocation. You may wish to hire counsel to make sure it is done correctly. Also it is a good idea to send her a verified latter advising her if the same and keep a copy. This response does not create an attorney client relationship. It merely advises you of possible options and I suggest that you hire counsel to make sure you are adequately protected from continued use of the power of attorney.