I'm a bit confused about a couple of things here-
Why would Airbnb e-mail the guest to say they did not receive payment but at the same time confirm they will refund payment - makes no sense whatsoever.
If we assume Airbnb called the money from her credit card whilst for some reason the reservation remained in pending stage, then refunding the money would not result in bank/ credit card charges; such charges are normally be as a result of lack of sufficient funds in the account or exceeding the authorised credit limit.
This guest did not actually book a reservation with you and even if she did, Airbnb would not release the funds to you until at least 24 hours after the guest has checked in. This is not the case here as such you never received any payments. Therefor this is a matter between the guest and Airbnb/ possibly her card provider. You do not need to get involved in the matter and frankly speaking, there is nothing you can do for the guest other than suggest they liaise with Airbnb and wish them the best in resolving the matter.
All the best, Ama