legal responsibility of break in?

I rent apartments and houses to people visiting the area for a month or two (it's like corporate housing).

I rented an apartment to a person named Sara for the month of September. On the night of September 26 or early September 27th, someone entered the apartment through an unlocked (and possibly open) window and took a laptop computer. The morning of September 26th Sara discovered the theft and immediately packed her belongings and moved to a hotel.

I called the police and met them at the property. There was no sign of forced entry and the police concluded that the window was unlocked and likely open.

Since September 26th I've been communicating with Sara's department coordinator, her name is Lisa. Both work at a large hospital.

On or about October 7th, Lisa emailed me and told me the police apprehended the person who took the laptop, but that by the time he was caught/confessed, he had sold it. She also asked me to reimburse the hospital the four nights that Sara didn't stay at the apartment.

My response was that I provide a secure apartment with windows and doors that lock, but that it is the tenant's responsibility to properly use them. If the window had been locked, the entire incident could have been prevented. However, as a gesture of goodwill I provided them with a partial refund.

Today I receive an email from Lisa. She now wants reimbursement of the entire balance from me. She also wants me to send her a check for $850 to reimburse her for the stolen laptop. They've started pointing the finger at me, saying that I was the last person in the apartment (to do housekeeping) and who's to say I didn't open/unlock the window?

I told her that I unequivocally did not unlock the window and had no reason to. I told her that if she seeks restitution of the stolen computer, to go after the person who took the computer and confessed to the crime, not me. Her employee caused this entire thing to happen, and they are looking for ways to shift the blame onto me.

From a legal perspective, do they have a case? I can't imagine any small claims court asking me to pay for this laptop, but wanted to get some advice before I made this assumption. Thanks for your help!