I'm not going to propose to my fiance in the same place both sets of her grandparents and parents got engaged
That can be a little sad. Why do you want to break the tradition?
It's time to get away from old fashioned stuff, don't you think?
Since you are aware of the location that her parents and grandparents got engaged, it seems you have discussed this with your girlfriend before. Instead of denying her a family tradition, you should compromise on the location and how the proposal is carried out. Compromising will ensure that the proposal is special for both of you.
It's not bad to do a tradition, just because other people did it and I don't want her to feel like she's not my priority.
Yeah, it would be nice to try and follow what her family did, but if you're not happy with it then it's really important to discuss this with her. This is a once in a lifetime event, so it has to be perfect for the both of you!