How to (girls)?

How do I know when my girlfriend s? During her legs begin to twitch and her whole body twitches, her eyelids even twitch, it's kinda cool but we're still not sure she's having an as there is no huge release, rather a tense buildup to twitching and good feelings. She also seems to hold her breath and push me away like the feeling is too intense. Afterwards she is weak and doesn't want to move but there is no real "". So my question is, how do you know when your girl s and how will she know? She "thinks" she has them, but I beleive what she is feeling is more of a buildup and "good twitches". From anyone experienced are there any tricks to get beyond this point? and do you always have to have a "pee feeling" before you .