Hello @Hayley-Nathan-Shelley-An0,
If the guest has already booked, do not cancel it. You will be severely punished (dates blocked, ineligibility for superhost for a year, and sometimes a fine). Similarly, if you receive a message "guest wishes you to cancel" so no hit accept. This is the same as you cancelling. If the guest wishes to cancel, she can do it independently, no problem.
If the booking is still in the inquiry phase (it is a bit unclear from the post), no need to do anything, The pre-approval will expire after 24 hours, and the guest will no be able to book. Also, she will only book if the wants to, so she is in control there anyway.
If you want to decline a booking because you are uncomfortable with the guest, you can do that with no penalty, as long as you do not decline several inquiries in a row.
Keep all messaging on the Airbnb message system always.