@Clara124, as @Branka-and-Silvia0 have mentioned, you don't have to do anything about the money; AirBnB will take care of it.
What worries me is each time you mention the guest cancelling, you also say you "accepted" it.
For the first you say "She initiated the cancellation and I accepted." and for the second you say "I accepted his cancellation".
The few times I had a guest cancel their reservation, I didn't have to Accept anything or even do anything.
The message just says "We regret to inform you that your guest (guest name) canceled reservation (reservation #) starting on (date)."
There are no buttons for me to push or links to click to accept anything.
What do your cancellation message say?