As you know, there are various BCP formulas and another one may be helpful, rather than harmful to her. The odds are that whatever is occurring is due to sex hormone cycling and as you put it, a biochemical imbalance. Blood tests assessed repeatedly before,during and after her periods, taken across several months, can help determine which hormone levels are abnormal.
The other issue of concern of course, is that your daughter is in the high risk period of life for developing a mood disorder that is independent of, or interacts with her menstrual issues. It might be that a mood stabilizer or antidepressant, taken throughout the month may help her a great deal.
Regardless of the physiological findings and outcome above, your daughter will no doubt, still have some mood regulation problems, as she has had for as long as you can remember. The clear message that you and her boyfriend can communicate to her is that: 1) it really does seem that your emotional roller-coaster and some of your unpredictable behavior are related to hormones and neurotransmitter imbalances; 2) since you are beset with these problems and we care about you, we want to help you fully understand how your emotional reactions and behavior affect the view that other people hold of you; and we would like to do what we can to learn to reduce the impact of your problems on your reputation, how you come across to people etc. This latter point of course, suggests that she will eventually benefit greatly from working with a clinical psychologist who specializes in an area called behavioral medicine or health psychology. These psychologists can be found in most large hospitals or medical centers, especially teaching hospitals affiliated with medical schools. The would be in departments of psychiatry, behavioral medicine, family medicine, women's health, etc.
If the visits to the endocrinologist or gynecologist doesn't seem to be pointing toward answers, the other issue as I said might be an emerging mood disorders and you daughter should eventually be assessed for such a problem e.g., bipolar
disorder II, cyclothymic disorder. You can Google these topics: DSM Bipolar Disorder; DSM Cyclothymic Disorder and read about the diagnostic criteria; if either or both seem to "fit" you should draw attention to this fact when you talk to the medical specialists, or visit the clinical psychologist-behavioral medicine specialist directly.
I hope this information is helpful to you. Let me know if I have overlooked any aspect of your question.