Could you try using to console to remotely shutdown her computer?
Run the console as an administrator
>net view
>shutdown -i
>click add computer
>type in the name of your sister's computer (it'll show up under the net view list)
>hit ok
>set to "shut down"
>Set delay time
>uncheck "notify user of this action"
>put in a reason (they will be in a drop down box)
>hit ok
This is just a very basic and temporary solution. Assuming you have Windows that is.
