@DiDi1
This a long term stay, so the long term stay policy automatically applies (overruling any other cancellation policy set). The guest has the option to cancel the reservation (do NOT cancel it yourself) and the policy will calculate the refund (which in general means she lost her money for the first 30 nights, useally also the first payment), as explained here:
https://www.airbnb.com/home/cancellation_policies#long-term
After cancellation you calender will be free for new bookings.
Best regards,
Emiel