the serial number should be on the box. if she registered it online for the warranty they may have it. When filing the police report other identifying marks may help like a large scratch in a certain area. the user name may help but windows passwords are extremely easy to bypass and it could be changed or they could just wipe the drive.
if she had any info like tax documents/passwords/credit card numbers make sure to do security freezes on her credit report watch for suspicious activity etc