Sorry I got in on this late. Try this next time. Get a program called Hide Folders. Its available here
http://www.fspro.net/
It's free for the demo version and is fully functional with minor limitations. Put all your stuff in a folder and hide them using this program. Copy the program files to a floppy disk and delete it from your hard drive. The folder with your stuff in it is totally invisible-even to searches. Without the host program they can't be made visible. After your sister-in-law leaves copy it back to your hard drive and un-hide your folders.