My gut response is, if you have to ask, she may be faking. I don’t know anyone who fakes o'rgasms—but then, I’m a New Yorker, and we’re a pretty direct breed!
But according to s'ex expert Tammy Nelson, M.D., 70–80% of women do fake o'rgasms (though how could anyone conduct an accurate study if the control group is composed of orgasm-faking liars?!). Anyway, apparently you have a right to be concerned. So many women fake it, says Nelson, “because they’re afraid or don’t know how to tell their partners what they need to achieve a real o'rgasm. Most women need direct c'litoral stimulation for anywhere from seven to 45 minutes, and unless she gives you hints—sighs, moans, ‘Ooh, yes!’—you won’t know if you’re even in the ballpark.”
But there’s a way you may be able to tell if you’re close, Nelson says: “When a woman’s arouse' d, blood engorges her v 'ulva, her v'aginal lips swell, she lubricates, and when she o 'rgasms her v 'agina pulsates.” (Or if it’s Siri, she buzzes like it’s an incoming text.)
That being said, O' rgasm Hunter, you could also look to her personality: Is she very accommodating in general? A people pleaser? Are her eyelashes real? If she fakes a lot, that may be a clue.
And if you still can’t tell, you can always just ask her.