I think female genitalia is a lot more complex than most of us give credit. Currently I am with a girl, I can make explode on a dime, because her G-spot clearly exists, and simple techniques will make her come on cue. On the other hand, I vividly remember an ex, who I tried quite hard to make orgasm in so many different ways, and she never could, and she had mentioned to me that she never had achieved one ever as well (this was even more of a reason to try). We did like each other a lot so that was never an issue, however when we talked about it and I probed a little deeper, it seemed that her gynecologist had mentioned something about how her Uterus didn't sit properly and had slipped because of weak muscles (the exact details I can no longer remember). On top of this she was never comfortable about sex in general, and later became a sort of nun. This is no joke. I later did some research and found out that if the uterus has slipped, which is common for a lot of women after pregnancies, they have difficulty reaching orgasm because certain nerves are either pushed or augmented by the change.
My understanding of all this in the end was simply, that, the G-spot might exist, but so many other factors can cause or not cause a women to cum. If you guys are having a good time now, and there's no problem, then bless your lucky stars. But if you're trying to find a specific reaction to what most people say they get when massaging the G-spot I think that is a futile search. Every woman is different.
Yet, I am convinced the G-spot does exist. And in general, I seem to find it most the time. It also happens to be a large area, instead of a spot. So massaging the area firmly and then perhaps isolating a spot in certain rhythms might hold the key, if she really is reactive at all in this regard.
Good luck.
