(1) never babysit for that couple again; and

(2) negotiate her rate before she goes to babysit

She was put in n a tough situation. I remember babysitting for a family in my ward that always paid me waaaay under the normal rate. The last time I babysat for them, their kids had a friend over who I also babysat. Of course, they didn't pay meany extra. The next day in church the mom pulled me aside and chewed me out because I had let the brats play an extra 30 minutes of video games. Had I been a little more assertive I would have chewed her out for not paying me extra to watch an extra kid. I still regret being polite and just taking the tongue lashing.