@Julie1516
May I suggest that should your guest request any form of refund to politely decline it.
Field mice & explain just like humans will do what they do.
You live in the countryside.
Perhaps find some cute story about a Field mouse, send a copy of it to your Guest & explain it's simply nature.
I don't think in any way you should even contemplate any form of refund as it's not like they were seriously impaired but simply having a natural encounter with nature.
Maybe also put a photo of a cute book with field mice stories on your profile and play on the fact you have nature in your property, some will be delighted.
As an aside, people dressed in Mice Coats in the 1930's when the Depression happened and a lady in England breed them expressly to make clothes.
You may like to look up that history & share it with your "Fear for her safety" guest.
It helps put things into perspective & makes one appreciate what we have!!
All the best from across the miles in Remuera, Auckland, New Zealand