Don't push. Because even if you try not to push, it will likely still feel like pushing to her. Just be patient and enjoy the journey. She likely needs to feel safe and that she has at least some measure of control over how things go. Nurture those feelings in her, and nature will take care of the rest. She already knows you want it. My guess is that if you lighten up on the "encouragement", in time, she will bring it up, asking you if you were really serious about that. It's a helluva lot more exciting when you know your wife is thinking considering it on her own, and knowing that when she finally does it, it's because she really wants to! But be patient. It takes time, maybe even a few years.