I never understood why someone would want a "partner" that they had to hide things from, especially a plant.
If the mindset of that person (your GF) is anti-pot, and you're pro-pot, it really doesn't matter how well you get along... the fact remains that she is ignorant, and you're not. Get rid of her if you really need to hide it.
If you have to question her integrity as to whether or not she would rat you out on a grow, get rid of her. If you have to question someone in regards to how they may dictate your freedom, that person should not be in your life, unless you like your freedom dictated by others.
Do as you please, but it boggles my mind as to how someone could be around another human being who would have a problem with how you live your life, if they're trying to be a part of it.