Tell you what you should do:

Go buy a paintball gun. Any one will do.
Get a huge tank of CO2. I mean like 32 oz or so
Get about 500 paintballs. If you're really feeling vengeful, get a case: 2000 balls for $60.
Get some night vision goggles and a red dot sight

Next time she comes over, I say have a little target practice. Note: turn the velocity all the way up. Trust on that one. And aim for exposed skin. Hope this helps