Many guys view women as a little bit unstable and this is not too far from the truth. The hormones and general make up of a woman mean that their emotions and emotional states are generally stronger than that of men. Add to this the fact that women have been penned into living up to many impossible stereotypes and it is easy to see why women tend to be more insecure than men.
(interesting observation of the hormonal effect http://www.newscientist.com/blog/lastword/2008/10/its-his-hormones.html#nbicomments 2nd comment from bottom)
Ok so women are more unstable than men, this means it is your job as a man to provide stability. You have to be the emotional rock that she can cling onto. That is not to say that you cannot be annoyed, but you know when an issue is extremely minor. If it does not matter concede the point (your "principles" are bullshit principles. not killing people is a priciple, not conceding a point is being a dick). Stay level and logical, if you have points to make then make them, and do not get drawn off onto other (even similar) issues. Basically, listen to her and ignore the drama aspect. If it is really petty, or something you cannot control, ignore it totally, treat her as you normally would and do your best not to be short or irritated with her.
Most women hate doing this, and hate doing it to people they value. Sometimes you have to give her a little space, once you know what she thinks she is angry about, say something to reassure her, concede a point or 2 so she does not feel like she is rolling over backwards for you, then walk away. It may take 5 mins it may take a couple days.
All this feels a little draining, you are giving a LOT of value doing this. Try to remember that you are the man and it is your job, believe me it helps. Also try to remember that to a large degree she will not be able to control herself. Try not to hold it against her. When she does conced a point or feel guilty for having the drama in the first place, reward her, this is a very noble thing for her to do and probably took a lot of effort.
There is a reason people say "be the bigger man" and not "be the bigger woman".