Checking for visited sites

Tell us which browser they're using. If they're using a private browser, and covering their tracks, you could do this to view the contents of their DNS cache.

If you email it, of course they can. It'd be in their sent email.

Presuming they're a typical Jane/Joe, they don't lock their computer when they walk away from it. That immediately creates the defense that the maid was on LookingForJody dot com, not your target.