MY DD is a CM in the Club. The info you've received is correct. You won't have a problem as long as she's potty trained and comfortable functioning in a 1-15 kid to counselor ratio.
Their job is to be sure everyone has a Magical or Wonderful experience not police ages. If she has a potty accident, they'll page you but she'll probably be fine. I do know they sometimes take younger potty trained children so you're fine.
Have fun and don't stress over it. The counselors are fantastic, but since my DD is one of them I might be "slightly" prejudiced.