The things with boundaries, is if they are good and strong in the beginning, as you get to know person in various situations, and see that they are trustworthy, you can loosen up a little.
However, in those situations where you are going into it not having good boaundaries (which happens to many people, not having proper boundaries modeled, or not respected, in childhood), and then you learn about boundaries part way through a relationship that isn’t going well, and try to pull back when the situation has already gotten messy, the other person is going to react to that. That’s pretty “normal”.
It can be pretty challenging figuring it all out, not sure if perhaps your gf is a “no boundaries” person, but I’d kind of expect a huge push back from her. Things can get hairy when you start implementing changes. And sometimes things do just end up naturally coming to an end when you realize deep in your gut there are certain things you can’t accept/ go back to. Good luck figuring it all out.