The Reply to Ad page is used by AWPCP when someone clicks on the “Contact <name>” link on the ad itself. That page is NOT one your users would click on directly. AWPCP will populate it with the data you need, but there’s no reason to put that page on a menu or make it publicly visible.
With that said, don’t make it PRIVATE and don’t change its status to Draft or something. That will break AWPCP. Just keep it out of the menus and don’t link to it. Your theme should provide a way to do that. If not, you can hack the theme to exclude that page in the menus.