You say that you've tried everything but you might have overlooked some details:
She might be a squirter who finds the "need to pee" sensation uncomfortable when you stimulate her g-spot so the holds her orgasms back. Is she educated about female ejaculation?
Rock hard erections apply more pressure to the trigger points, do you always stay extra hard?
Diet can effect orgasms and sensitivity, especially alcohol. Food that improves bloodflow will help fill her and your "bits" full of blood. Have you tried aphrodisiacs?
Vigel Sex Gel for Women - topical sex gel L-arginine for orgasms! How about trying this orgasm gel
Choose sex positions that "hit" the g-spot and epicenter - pressure on these areas triggers orgasms. Have you tried wedging your glans into the epicenter and applying pressure with short but powerful thrusts without dislodging the glans?
The clitoris and AFE zone, react to friction so try positions that that rub these areas.
Women are more orgasmic during ovulation, so make most effort during those few days.
There are other things that could be effecting her hormones, she could have very low testoserone levels, do some research and maybe blood tests.
I think that you should just keep focusing on the 4 orgasm trigger spots during sex and lower your expectations, she might end up surprising you.