I have gotten some flak for my take on this. But I'll comment anyway, others are free to disagree. I'll just throw out some thoughts on different aspects of this. She needs to get a full physical including blood and hormones. Diet and exersize are critical to all levels of health.
I have someone close to me who deals with this and has pretty much all of her adult life. It can be very difficult to be around them you never know what they may go off about. However I've known males to exhibit similar patterns, so I have some doubt as to this being a "female" problem but believe we just perceive it differently in the two genders. Is it hormone related? Probably. But then just about everything in the body is.
Here's something I've noted with many people that gives me pause and we had some discussion about it here; if they can control themselves around some people (like the boss) or in some situations (like dealing with a client in a money making situation) but lose it around family, lovers or freinds or sometimes strangers, how many times have you seen someone go totally off on a store clerk? - then they can control it. They may have internalized the belief that they can't or that it's ok to dump on some people but not on others, but they are at some level controlling it, albeit not consciously. This may have a cyclic hormone factor but looks like it has far more to do with poor stress management skills.
I know the current trend (strongly encouraged by the drug manufacturers) is to medicate for everything. I disagree with that in most cases.
The flood of chemicals and toxins we are exposed to daily probably play a role. As MCS sufferer, I aware of how some substances can act as depressant on me and no doubt do so to others - but they may not be aware of it. Adding more chemicals to the mix just doesn't sound like a good solution most of the time.
Women I've known with pmdd, who have the depression, lack of energy, aches and such don't seem to have control over that, although something that they are really excited about and looking forward to often can carry them past it (it releases the endorphines in high levels). But in the ones who really get in rages, it often seems selective, being pissy is one thing, getting down right ugly is another. Women on the whole have plenty of reason to get POd, righteously, but not to lash out. They need to find healthy outlets. A punching bag, running, primal screaming, firing off a few letters to their congressman, some constructive ways of expressing their frustrations. Displacing it on to those near and dear is a really bad pattern.
When I'm down, everything gets me. When I'm Up, almost nothing does and I think this is true of most of us. Woman are still unlearning generations of suppression and misuse - some of us have developed odd ways of coping, as have some men when they are thwarted or feel put down (think alcohol, porn, abusive behavior). Perceived/internalized powerlessness can result in some very negative responses. While it is overt, I see this as a passive aggresive behavior because the responsiblity is passed to something or someone else.
We have to own the problem before we can solve it. If it means a lifestyle and diet change, reducing exposure to toxins as much as we can, maybe a move, then we need to look at that. Everything has a cause, a reason. Nothing just happens. Modern life causes many to live with huge amounts of stress, we seem to think we should all be superpeople. Women deal with the seeming conflicts between being a "good" mother/wife/feminine person and being a "good" employee/business person. Our societies still hold a largely male based business model which works pretty well when you have an unpaid partner in the background.
All this aside. If she won't talk about it or get help to deal with it, there isn't much you can do.