Legal Question in Landlord & Tenant Law in California

None.

If there is no proof as to when the laptops were stolen then you can not establish they were stolen at the party. Legally, if the roommate knew or reasonably could know that the laptops might be stolen she would have to protect against that occurring, either by putting them away in a safe place or looking when people were about to leave if they had a bulky item on them. But if you knew that that might happen, you also would be negligent to some degree. Without more facts, such as where the laptops where, the size of the rooms, the reputations of the guests, the precautions taken to prevent stealing, etc, whether there is any liability can not be answered.