If you have renters insurance, you should call and explain it to them. You probably have at least $500 and possibly $5,000 of no fault "med pay" benefits that can be used right away to help the guest. Also, you should give them your landlord's info, and the info about the prior repair etc. Dealing with this kind of thing is what you pay them for. They will call the guest, the house sitter, the landlord and try to get more information. If they think it isn't your fault, they will try to get other insurance to pay.
It probably will become a legal mess. Nothing you can do can prevent this. Be sure you are honest, and don't have to change your story later. That gets people in trouble.
It seems pretty obvious this is not your fault. However, it is going to be your hassle. That's not fair, but it is true.