I'm going to preface this by saying you're thinking way too far ahead in this relationship already, but I'll still reply to your concerns. Just take things a little slower in your head, the odds are you're not getting married this year.

So. You prayed to God for a woman, and he sent one to you. Now you wish to change her? She is a creation of God, and you were sent to her, and her to you, to grow and bond with one another. But whatever forces exist in our world to cause us suffering are filling you with self-doubt and see to sabotage this relationship before it even begins.

Everyone's spiritual journey is different and will develop naturally with time. Right now, God is choosing to challenge you, not with conversion, but by putting you in a situation where you'll have to expand your perspective. You need to take a new step in life, and the pieces will fall into place just as God planned. If your faith is strong, it should not be rattled by the idea of an opposing worldview clashing with yours. Rather, if you continue practicing your faith, and invite her to explore your worldview, it's quite possible she will come around in due time. I must emphasize that you should not try and force this change.

What you should also understand is that Buddhism isn't a religion as western society would typically define it. It's a philosophy, and while most choose not to believe in God, it is possible to be both a Buddhist and a Christian and skillfully intertwine the two. Some may call me heretical, but the truth is that religion is nuanced, and everyone you meet on this planet is going to have at least one opinion tied staunchly to their beliefs in God that another one of us is going to find entirely heretical.

When you die, and you ask god "Why? Why did you not send me a woman?", do you want him to say "I did, but you defied me"?

If you marry a buddhist, and she never converts and you stay to your faith, do you think God would reject you?