Well i would suggest you try to get your Sister-In-Law to grasp the advice given by patcooke. I mean, you can't really do anything remotely, can you, since
ye have not the password. Unless you want to create a carrier as a hacker?
... then, nothing would be impossible.
Another option is, ask Microsoft. If the program is legitimate, they usually show great understanding, and they do have a great customer service. Besides, they have all knowledge there is. Make a phone call, be sure to have all receipts with registration codes etc. at hand. They actually have the capability to reload the entire PC, if you give them your = her e-mail.