Do you mean "A guy asked my girlfriend to a prom?", than no, she shouldn't go. If she is going to a prom from her school and no guy asked her to go, than yes she should go. It will be hard trusting someone young, but I wish you both luck and a relaxed life.
You shouldn't deprive her of her childhood. Prom is so much fun. Believe it or not, girls go for the experience of Prom. Sometimes it doesn't matter who you go with. I went toy first Prom two weeks ago and there wasn't anything wierd or awkward about it. It was me going with a friend of mine and a group of other friends. It was a blast and nothing happened that, if I had a boyfriend, would make him mad. Oh, and thank you for what you're doing for our country.
If she didn't go to her prom and their just friends sure. I mean you trust her right? I'm so sorry for how ride people are being to you, when your fighting for their freedom. Thank you so much for what your doing for us. And as for your girlfriend, she probably loves and misses you, but let her have a little break from being stressed out and worried about you for one night.....it can be hard on us at home who miss you guys to! :) if your really worried about it ask her not to, but their probably just friends so I wouldn't worry about it to much she should have fun