@Lily241 You should contact Airbnb to say you are still seing that the payment from the guest hasn't been made and that unless they can assure you that they have secured payment, you obviously can't allow her to stay. Also let them know that she is not answering your messages. Don't let them put it down as a host cancellation, though, you'll be punished for that.
I would suggest that you set your advance notice for 2 days on your calendar. That way, you won't get these last-minute bookings that may or may not be paid. There have been posts here from hosts who haven't been paid although the guest stayed, for exactly the same scenario that is happening to you right now.