Well, I'm not sure how you figure out what she likes by stopping having sex so I'll suggest that you experiment with her and ask her to guide you. Maybe if you watched her masturbate you be able to follow her lead. Get some toys and play with them together.
I doubt very much that you're getting her off through intercourse if you're not getting her revved up enough to actually cum. Most women need clitoral stimulation and if you haven't figured out how to rub her clit while thrusting your rod and your staff that comfort her then I doubt she's really finishing.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion