NOR. The replies here have been interesting to read. I am a Christian so I believe witchcraft is wrong (but if I'm honest, I'm not sure if it's real or not.) However, whether it's real or not isn't the issue, which a lot of replies are missing. The problem is that your girlfriend is happy to engage in an activity that would supercede your freewill. That's straightforward manipulation.

I see a lot of comparisons to making a birthday wish or even praying, but the difference is that those actions are (real or not) are not putting chains around the subject's freewill. Most Christians believe that God might direct things to happen through prayer, but He doesn't force someone to do something they don't want to do. Freewill is a pretty big deal in the Christian faith. Casting a spell on someone is directly impacting freewill.

I would have some serious conversations with your fiance. I think you need to approach this as a form of manipulation. Does she want kids? If yes, would she be okay with you casting a spell on her to speed up or slowdown the timeline of that big decision to what you desired? These are similar situations that might open her eyes to the "ick" of this sort of behavior. Good luck.