Forks Township Police Department say 31-year-old Fallonn Craig of Easton, Pa. has confessed to setting the fire at the building, which dates back to 1830.
Craig is being treated at Lehigh Valley Hospital Cedarcrest and will be held on $250,000 bail at Northampton County Prison after completion of her medical treatment.
Police say Craig admitted to setting the fire as a result of a domestic incident.
She lived at one of the apartments above the Mineral Springs Bar.
Four people were injured in the blaze.