@Pam169 do not cancel, as host cancellations are heavily penalized.
You certainly should tell the guest that you do not allow hot plates in the Guest Suite. Remind her that there is a microwave provided for preparing food, and say that the microwave is the only approved heating device allowed.
(Maybe add "No Hot Plates" to your house rules.)
You are in a little bit of a spot because if the guest is not agreeable and pushes back, you did not explicitly have the rule in your house rules before. If it gets to that, then at that point you should involve Airbnb and ask if they will support you on disallowing the hot plate.