I'm one of those strange women who almost never squirts from g-spot stimulation. When I squirt, it's usually from the kind of hard, fast clitoral stimulation that makes a long, screaming, thrashing, arching, never-ending orgasms (I usually don't squirt until a few orgasms in though). If there's some vaginal or g-spot stimulation in there, great. If a penis gets in the way of the stream, then it doesn't go very far. The key with me seems to be intensity and duration of the orgasm: it's gotta be earth-shaking, and it usually has to last at least a minute before the tsunami hits. If I've started speaking in tongues, you're on the right track.
Unfortunately, as you can see, women vary greatly in what gets them squirting, from g-spot only (hard or soft) to clitoral only, and everything in between. Just experiment, and aim for what makes her feel the best. If it doesn't make her squirt, at least she had a heck of a great time. If it does work, take notes (with a waterproof pen!); you may have just found her special combo. Have fun figuring it out!