I'm going to say one more thing, and for all my advice is worth hopfully it will serve to keep you from acting like a complete idiot in front of her. You should be wary taking some of the advice you have been receiving.
Show your confidence with the knowledge that you, and only you, will be going home with her afterwards.
Whenever another guy approaches a girl you are with or dating you should always respond with humor. Sit there with a big smile showing your teeth and watch the guy try with all his effort to win her over if he absolutly thinks he has to hit on your woman. In the end it is up to her anyways, and you want to know why? You're just going to have to trust her.
Whenever another guy approaches a girl you are with you should always respond with humor. Anything else means insecurity and weakness.
And when you get home or alone with her say something jokingly, like for example "Hey, you think maybe he thought you were hot?" and wink at her or something. If you say it with the right stress it can have a real good effect.