A few comments before I make a suggestion about working with anger overload. If her episodes of anger overload occur more frequently when there is a downturn in mood, it would be wise to check with a professional to rule out a co-existing mood disorder. Also, you mention some previous causes (changes in her life), but suggest the anger problem continues even though there do not seem to be any particular causes right now. You might want to chart the next three episodes (I discuss this in an early chapter of my book as well), and then look for any patterns. Does it happen when the attention is on someone else in the family, or when she is feeling lonely? You mention her sister's diabetes and her friends moving away, so I wonder if any of these issues might still affect her. Or you may find there is another issue which precipitates your daughter's outbursts. If you see a particular type of trigger, then you can try to address that.
Whether or not there is an obvious pattern, you would want to enlist your daughter's help in understanding this problem. As I suggested in my last post, there are ways to bring your daughter's attention to the problem without being critical of her. When she is calm, you could point out any possible trigger you see, and ask her to consider if this seems correct. If she disagrees, ask her if she has any ideas. Also, help her see when she is "heating" up next time by labeling the level of her anger (as I discuss in last week's post). You are trying to get her to continue to think about the problem. Bring this up as an issue you can work on together in the next few months.
For pre-teens and teens, it can be helpful to head off outbursts by discussing potential pitfalls and alternative solutions. You can do this if you see some patterns. You can talk about an issue from both your point of view and hers. State what your concern is (for example if there is tension about homework or curfew, state why you have a certain rule) and then ask her what her point of view is. You are trying to head off major conflict (assuming this is a cause of overload--let me know if there is some other cause and I'll try to advise you), and help your daughter begin to think about how there are different points of view. Then you pose the question: how can we work this out? You try to engage her in a discussion (when she is calm) about an issue and see if you all can come up with an alternative (compromise, if the issue is negotiable) that meets everyone's concerns. You are helping her then not only identify an issue but practice working it out ahead of time.
When overload occurs, it is best to avoid these kinds of discussions and encourage "chill" time. Some kids chill with music, some by physical sensations (squeezing or holding something), some by music or drawing. It may take some time for your daughter to discover a way that works for her, and you do not want to suggest too much, because it is best if she comes up with something herself. After she calms down, ask her how she did it and reinforce her approach if it was effective and if it did not involve harming herself or anyone else.
One possible biological change that my help in the coming years is the continued growth of her frontal cortex, the part of the brain that controls emotions. This growth will continue even into her twenties, but the strategies I have outlined can help this process along. I will continue to post more strategies in the coming weeks.
In your addendum (which I just read but did not print above), you mention she gets headaches and feels tired sometimes before or after anger overload. I have noticed that anger overload sometimes occurs when kids are tired, but have not noted any correlations with headaches at this time. Certainly when kids are tired or not feeling well, they have fewer "resources" to deal with stress. Furthermore, anger overload can be draining (like running an emotional marathon), especially if it goes on for more than a few minutes. If you continue to note a correlation with headaches, I would mention it again to your doctor, and follow his lead, as he knows your daughter's situation better than I. Hope this is helpful. Take care, Dr. Gottlieb