Airbnb does not get into the business of solving “guest said, host said” types of arguments. I know this seems terribly unfair, but I understand why Airbnb needs to stay away from that.
The best you can do is scrutinize Airbnb’s review guidelines and see if there is anything in the review that violates their review rules.
Also, and this is very important, respond to the review publicly. Keep it professional and brief, and remember it is aimed towards future guests - the past guest might not even see it. Just calmly state that you are sorry the guest’s needs weren’t met, you wish the guest had contacted you if they had requests, and that there are indeed large blankets available.