Remember to check high places too, like the top shelf of any closets. I'm fairly certain that as soon as a ball excapes they grow wings to ensure they won't be caught. Little turds!!
I would sure be telling my parents my sister needs to get rid of her ball if she can't take care of it. That's a bunch of diddly that you get blamed for her being unresposible.
How close is feeding day? Have you tried scenting it out with a rodent?