Women fake orgasm's for the man's benefit, not their own. Unless, maybe, they just want you to stop. Which, could be to their benefit if you were lousy in bed I suppose.
I've slept with women that would orgasm at the scent of bleach, and I've dated women that I literally had to teach them to relax their brain enough to orgasm.
If you want to know if her orgasm is real: Typically you can feel them contract, and the truth is 99% of women hold their breath during orgasm rather than scream out. They might scream out after, but really you'll usually hear them suck in their breath, and hold it for a few seconds before they start going all Michael J Fox on ya.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."