@Jennifer1919 I would agree with @Gordon0 about not being too tied up or verbal in your reply to your guest.
Before booking that discount your guests would have considered the implications before choosing that cheeper option and plumbed for the savings. Now if they had booked the higher cost option they would have been able to cancel entirely at your expense and would not have hesitated.
The wording from Airbnb in their refund message to hosts is deliberately confusing. They ask something like.. "Do you accept your guests refund request..." You obviously do accept their claim, but you do not accept to refund them or be responsible for it. The answer would be 'No' You do not accept the refund request. If some other host here has the specific wording for this, it might help to clarify how the wording is confusing (?)