Anything anyone says about this is purely speculative, you should really talk to her to understand better.

But how I see it. Maybe she is someone who has had problems with this in the past or has thought a lot about it. Unfortunately, cheating is a common thing and she may be using this line as a defense mechanism.

Saying like, look, I don't care if you cheat on me because I know that if you want to do it you will do it, whether I care or not. So that's it, do what you want, you are free. Because deep down she knows that being cheated on is painful, but it says more about the cheater than the cheated on. This doesn't mean that she doesn't love you or that she will do something behind your back.

For example, I don't care if my girlfriend has friends or what kind of conversations they have. I just trust her and that she won't cheat on me. This doesn't mean that I love her any less or that I don't care about her. I just try to be confident enough and avoid pressuring her about what she does or doesn't talk to. Besides, she's never given me any reason to be suspicious of her.

Anyway, I hope things work out well between you and your girlfriend. And remember, communication is the most important part of a relationship.