@Peter1888 Airbnb cannot take money out of your bank account. That would be highly illegal. What they mean is that they will deduct the amount from future reservation payouts, or if you haven't received the money yet for this reservation, they will just deduct it from what they would have paid you had the booking not been cancelled.
However, most hosts advise against refunding money to guests through the resolution center until you have actually received the money for the reservation. Because sometimes a host refunds money, only to find out that the guest has also applied to Airbnb for a refund and gotten it. So they have received the refund twice and you're out-of-pocket for the money you refunded.
I'd maybe contact Airbnb to make sure that the guest did pay for this reservation in full (rather than half-up-front) and that if you send her a refund through "Send money", it will cancel out the $ that is supposedly sitting in Airbnb's coffers waiting to be paid out to you.
A lot of guests think that as soon as they pay for a reservation, the host has their money. If they are asking you to refund, or you want to offer, it's good to make it clear to them that you don't have their money at this point, therefore there is nothing to "refund" -that Airbnb has their money and hasn't released it to you yet.