Well for starters the facility clearly has a security issue , that should not be taken lightly by the staff. I would inform the adminisration if the staff has not already done so. There should be some kind of camera used for security purposes. if you know the dates that the quilt was last seen . I would ask that the least they should do is review those tapes from the time period. Some might be reluctant to use manpower this way ... but it is a theft and should be treated as such. It it begs the question as to other issues in the facility if this is not treated seriously.
At mimimum there should be compensation for your materials, though that hardly is the real issue.
An interesting note is that this happened when you Granny was in a declining condition, and it sure would appear that someone took advantage of the situation, which would also be of great concern to the administration.