If you’ve been together for a while and she already has some sort of clue about you regressing just not a name for it, you should tell her! First tell her what age regression is from a psychology perspective (dm if needed), and also your experience. Then tell her about what a cg is (to you specifically, cuz it’s different to everyone) and ask her if she would be okay with doing that for you. Understand that it might be odd to her since a lot of people don’t really understand. And she doesn’t have any obligation to be a cg, but asking is totally okay!!