Well, McAfee survived the purge. I looked up how to get rid of it again, went with one that was not tied to the company. Turns out I had to not only uninstall it, but also remove it from each browser in turn (though some seemed to not have it), by removing it from the search bar thingy. For each account, including the guest account. Speaking of which, now that Amy has her own account, I have turned off the guest account.
So as far as I can tell, it is entirely purged from all accounts. I will not be pressing charges this time, but if I do see it again, I may reconsider.
It's like cockroaches! Kill em one place, they keep coming back. Hopefully I got the last of that bastard program.