A cease and desist letter does not have to come from a lawyer, and it does not need to be notarized. The woman, herself, could send a cease and desist letter. if course, if it comes from a lawyer, it may carry more weight. If you receive a cease and desist letter from a lawyer or law firm, you can conduct simple on-line research to determine whether the lawyer and the firm are legitimate. For example, you can check to seek the lawyer or lawyer are registered on this web-site or linked-in. A simple google search should sufficient to provide you with meaningful information about the lawyer or law firm. Many, but not all, reputable lawyers and law firms are listed in Martindale Hubbell.
But regardless of whether you receive the cease and desist letter from this woman or a lawyer, you should retain counsel in Ontario to represent you. You need to obtain objective advice from counsel concerning the claim that you engaged in copyright infringement. Your statement that you did not infringe is not what matters---what matters is whether there is a risk that a court could find you to have infringed. If there is no basis for the cease and desist letter, your counsel can respond appropriately. If there is a basis for the cease and desist letter, or if there is a risk that a court could find that you have infringed, then your lawyer can try to resolve and settle this dispute. The amount you invest in legal counsel will probably save you a much greater amount in the long run.
You've gotten some good input from Mr. Ross and Ms. Hansen. It probably doesn't need to be said again at this point, but I'll reiterate that you should speak with a copyright lawyer in Ontario about the situation immediately and without communicating further with the woman. It may all be nonsense as you believe, but her claim could create real legal problems for you, and having a lawyer help you from the beginning will likely make everything both less problematic and less expensive. Good luck.
The information provided here is general in nature, is not legal advice, and does not create an attorney-client relationship with Will Montague or Montague Law PLLC.