Open Task Manager (ctrl/alt/del)...see if there's a LimeWire process running. If there is, end the process. If you've been trying to uninstall via Add/Remove Programs, that's the wrong way & can cause problems. The correct way to uninstall is via Start > All Programs > Limewire & use the uninstall option.

If you've tried to uninstall via Add/Remove, you might have to use your computer's search to look for all files & folders with Limewire in the name & delete that way.

If you continue to get the popup after LW's uninstalled, ask your sister whether LW was popping up all by itself & refusing to stay closed. If that was the case, you probably have a worm & should read the post below
http://www.gnutellaforums.com/273873-post2.html