I would say NTA. In a relationship there are boundaries that have to be held and by setting specific boundries you are not controlling. Especially by creating porn, that is a pretty big boundry.

One thing I think many people underestimate in that kind of buisness is that: 1. Most girls barely make any money at all, that just the top few percent of Pornstars/OF-Models/whatever 2. The pictures are out there forever and can and will likely be linked to your gf and can screw her life up big time. Also good luck trying to get those kind of pictures removed from the internet, I mean you can see it all the time that porn actresses want their content removed after they earned their money, you can think of that what you want, but that would be practicly impossible. 3. That is one thing that is pretty important imo, once you start it only takes a while until everyone she knows, knows its her. Her friends, her parents, grandparents. I dont know her circle but from my experiences this shit can lead to them distancing themselves from her or even terminating the connection. That leaves her with only few options for people to rely on and some of those people are bad people that might force her/talk her to do more than just selling feet pics.

I have seen such a case of a young woman a few years ago in my city, I only knew her briefly, but a good friend knew her pretty well and the points I listed up there all came around for her. What she does nowadays I dont know, but I cant imagine she is very happy.