It should be possible to copy the files from the disc to a USB stick. Simply put it into the drive of the Windows 7 laptop. If it tries to autorun, simply cancel the program that starts up. Then go to 'Computer' and right-click on the icon for that drive and select 'Explore'. That should display the contents of the disc, which can then be dragged-and-dropped to a USB memory stick, which can then be transferred to the new machine.
If your sister still has problems she doesn't need Microsoft Office anyway. Se my post here for the free alternatives (which are just as good):
http://www.theanswerbank.co.uk/Technology/Question1391444.html