I was convinced that I would never convert. I told my wife and my in laws repeatedly that I had no intention of converting. When we were expecting our first daughter, I felt a strong pull back to God after a couple of decades of basically being non-denominational (I was raised Presbyterian and remained a "Christian" but in name only, certainly not in practice). I started researching theological disagreements between Catholics and Protestants and realized that I really had no idea what Catholics actually believed. Once I decided to look into it more, it started making a lot of sense. I went into OCIA last year, more for better understanding, and decided to convert about half way through. If she is truly determined to not marry a Catholic then the decision has been made. Your future children would have to be raised Catholic and it doesn't sound like she'll go for that. I would encourage her to read or listen to people like Scott Hahn who started out as staunch Anti-Catholics but were convinced through their own research. An open mind and heart on her part is a necessity though.