I'd try for 50/50 but ultimately dd would have to pay 100% if roommate is unwilling. DD didn't have insurance? It is a sticky situation because the dog has the run of the property when roommate is home and a dog is unpredictable. There is an assumption of the things that can happen with the agreement to allow the roommate to have the dog. The glasses were in an unusual spot and may have fallen to the floor before the dog found them too. Personally, if roommate is unwilling to help with the cost then in the interest of preserving the peace I would not press it. But I'd want to make some rules regarding future responsibility for the dog and any destruction caused by him (like pet deposits or refunds, property damage, spraying etc.).