I have a feeling that some of you people saying things like this aren't really reading the OP fully or just don't care, and instead just see a faintest hint of oppression attempt and immediately concentrate on that.
I know that might come off as condescending but I'm honestly not sure why you'd post like that otherwise. If I'm wrong then please correct me and help me understand. And yes I know the society sucks for women in many ways and men are often way too controlling towards women. But you should still be able to separate genuine concern and basic relationship functions from patriarchy.
Talking about things is what you do in relationships. Like, if I suddenly decided to somehow want a lot of tattoos, I'd talk about it with my wife because I know she hates tattoos. She'd have to look at them for the rest of her life so of course I'd listen to her opinion. It'd be pretty weird too since I also hate tattoos, so she'd be rightfully concerned about the sudden change of mind. Anyway, she'd probably voice her displeasure but ultimately be understanding, and to make it easier for her I'd probably start out with only very few tattoos even if I wanted my whole body covered.
It's obvious that the choice is OP's girlfriend's to make (and in my hypothetical situation mine), but you're in a relationship together and you have a right to voice your displeasure about things even if your displeasure is seemingly irrational.
In OP's case there's also the question whether or not it'd really help the situation at all or would the girlfriend still remain insecure. It seems unlikely that it would undo years of brainwashing. That said, it is a very minor thing so it's not like it's that big a thing.
OP, I'd honestly recommend to find her some therapy. Such brainwashing is a nasty thing and it'll likely keep haunting her for a long long time otherwise.
edit: I mostly agree with the post above. If she really is set to do it, be supportive and be there for her. But still remember of course that it isn't some magical solution to her problems.