Why is she scared exactly? Does she fear child birth? Or just isn't ready to be a mom?
Ultimately, it is her choice. It is her body and she is the one that has to go through child birth. All you can do is inform her of the other options, etc( not in a twisted way in order to get her to do what you want). If you can't support her decision, then it might be time to end the relationship.
Just my honest opinion.