Is this on a laptop? The track-points (the one that looks like an eraser head) are known to drift at times for no reason. Quite common, quite annoying. No real "fix" for this, just let it do it's thing and it stops tugging after a few seconds.
Optical mice can get the 'jitters' at times, and the only real 'cure' is to find the surface that works best to use it on. Mine works best on a wooden desktop, while others have found their optical mice to work best on a 'cleaner' surface.
If it's jumping from spot to spot as she works, check 'Mouse Properties' in case there's simply a 'Snap To..' function enabled that's causing confusion.
Otherwise, check the machine for Spyware and other malware.