@Zoe34
Hi -first of all a guest cannot leave a review if they do not stay. So you should have immediately contacted AirBnB and asked them to remove that review - perhaps you did?
Personally, I would give them some type of refund. Stuff happens and I can understand how if I was in her shoes I might not want to stay. But of course you have lost the chance to sell the room for the weekend.
I know there are other hosts that would be much more strict - but I would give maybe a 30% refund and explain that you lost other bookings. Perhaps also say that if they want to rebook for another time you will also give them an additional discount at that time.
I don't believe this guest will be able to leave review either - as technically they did not stay - but they did check in....so not sure..