Hi @Kayla527,
My understanding is all long term stays are on a strict cancellation policy so once the reservation starts, there is no refund unless there is grave issues with the listing.
The guest expressed that she was happy (I hope this is all on the airbnb platform messaging) so there is no reason to penalize you, the host for her error in deciding she wants a closer place to stay at. Many people nowadays are fickle and they think if they misrepresent our listings or outright lie they can skirt the system. It’s unfortunate that I’ve seen this in many host comments that the guest lies to get their way.
The best thing is to do reiterate that you are sorry she is leaving but there is a strict cancellation policy which means no refunds as she blocked your listing for bookings during the busiest season of the year. If there are bookings, offer a partial refund like mentioned by @Mike-And-Jane0.
I also would proactively call Airbnb support and explain what happened so it is on record your side of the story before the guest will call to complain and see if they can get a refund (and tell her side of the story or alter it - so it’s best to get ahead of her in this case). Good luck and let us know how everything goes.