Some of the symptoms of your girl's orgasm:
1. Moans and groans
2. Heavy breathing and body movements
3. Complete relaxation after the spasms are over
4. May not let you touch, stroke or feel her body/vagina after she comes as the original feelings are replaced by a ticklish feeling. You'll have to carefully maneuver yourself to get your part done if the orgasm was not simulataneous. In such a case, holding her tight (as opposed to the gentle touches earlier)while entering her will distract her from the ticklishness.
5. There is a disadvantage in a woman getting an orgasm - in some cases she will not want sex for some time as she's satiated. So its much better to bring to the peak and let her off and complete sex (they don't want a climax all the time) if you want to have another session later or even the next day!!!!
She should definitely know! I had my first orgasm before I married when dry humping. It was very intense and out of this world. Its good if you can try to get her to climax and O before intercourse. I find it harder to O then.
Believe me, if she has had an orgasm, she will know and you will probably see a different and more intense reaction in her, including a red flush on her face or body, intense quick breathing and heart rate and a change in her body tension.
I would stroke her longer, asking her when it feels intense, when it is not particularly exciting. Try stroking the whole clitoris- not just the little part that you can see, but the whole 'stem' of it that you can feel when you follow up from the exposed part with your fingers. Also, try using a vibrator with her while you are touching her or instead of touching her-- or get an internal vibrator ( put it in her vagina) and touch her while you are doing that...
Once she learns how her body has an orgasm, you will too, and it can become more regular.
She should know if she has or not. If it's a true orgasm, it's not something you can overlook or not realize.