Your forgetting (or don't know about) the single most tell tale sign of a female orgasm. Their chest area between their tits and under their neck turns red. This is a proven scientific fact that can't be faked, look it up. It may not be all that visible if the girl is really tan or dark skinned but it happens.
Don't believe me? Next time you fuck your girl do it with the lights on, and after you think you've gotten her off good look at her chest. It will be red, like her chest is blushing.