She has seen a cage before, on me in fact, but saw it as a short term thing and only played along for a few hours before she wanted to have sex. I was pressuring her a lot with it and trying to fufill my needs with it.
She is the one who desides when we have sex. If she does not want to, it does not happen...ever, and when she wants it, it better happen. That being said, once I find a cage that is comfortable and works for me for 24/7 wear, I will simply give her the keys in a passive manor, such as leaving them sit out with a note saying, "For when you want to have sex." She will know what they are for and it will be up to her to do what she wills.
From there it can grow as she lets it and we will do as she wants, because that is the point and all I want. Her to hold the key to my cage so that I am locked and have 0 control unless she needs my cock for her pleasure. Beyond that, it is her's to use as she pleases. If she wants to tease me, good. If she wants to go out on dates with my key hanging in her cleavage or on her ankle, even better. If she says no I just leave the keys sitting out and wear the cage and let her see how things are with me locked up. Will take a lot of self control from me, but I'm willing to bet that she will like having the increased non sexual attention with me locked up and enjoy my altered attitude about sex with being lock up. (Something I earn and not just expect and nag her for.)