Hi @Tina60
If it is outside the strict cancellation policy cutoff (I wasn't clear on that) why not just ask her to cancel her reservation it's by far the easiest way to go. She will be then be refunded everything she paid except the airbnb fee and no penalty for you.
Note: Do not cancel the reservation yourself, the guest must do it. If you do it you will be penalized and possibly fined.
As for questions:
1. I don't think so.
2. If her cancelling is not possible due to your policy ask her to send a screenshot of the amount she paid in Euros, it will list amount in Euros including the Airbnb fee, which is not refunded. As the exchange rate fluctuates it's probably the better way to go. Although currency exchange can be a tricky thing with hidden fees for conversion. So maybe better to call Airbnb so you don't end up paying back more than was received.
3. Search on this forum for "Contact Airbnb" there is a post with all the many ways.
Best