I would have to say, yes, do forgive her. The security guard was the one who was in complete control of his senses and should have acted professionally. He could have grabbed her hand, with the understanding that she was tipsy. I would also think that if you had kept your eye on him, he was probably doing the same thing to other women who had too much too drink. In this instance, I would forgive her. I wish you all the best in your relationship.
Another thought I had was again about the security guard and his clear advantage over the situation. Had you approached him, he could have used his power to say that you were overreacting. Might he have thrown you out of the club? Who knows, but he would have had that choice. My guess is that he spends his time macking on other women who are intoxicated, too. In this case, he's the one at fault. Also, what advantage would you have if you did not forgive your girlfriend? Not forgiving her would continue to cause a divide between the two of you. So my advice would be to just let it go and move on. She's with you, not the security guard who abuses his power to make himself feel better.