Hello @Natalia419
You can't prevent a guest from leaving you a review (see Airbnb Help Centre - reviews to help you understand how reviews work on the platform).
Message the guest back via Airbnb and say you are sorry to hear that she will no longer be staying with you as she had missed her flight. And that if she wishes to cancel, this would be done in line with with cancellation policy she has booked under.
I don't really understand the point about the guest not cancelling because she would lose her discount?
You don't need to let Airbnb know separately.