Hi, Children with ADD tend to be somewhat impulsive, such that when they get frustrated they sometimes act before they think. What you would want to do first is keep track of what is going on before she erupts. What are the counselors asking her to do, or what is going on when she yells at her bunk mates? Similarly at home, what is going on with her brother or friends before she loses it? If someone keeps track of that for a week or two, you might see a pattern for some of the times she gets angry. In my parent's manual, I explain ways to deal with outbursts--sometimes "changing the sequence" of events to minimize frustration, sometimes "emotional distraction", and sometimes ignoring.
The idea with technique called "changing the sequence" is to avoid the triggering event. For example, some children have trouble going from a fun activity to a task like cleaning up or getting ready for bed In that case, I would recommend doing the clean up earlier before the fun activity starts. For bedtime routines, it is more difficult to insert a fun activity at the end, since turning out the lights is usually the last thing an adult does before a child goes to bed. But what I recommend is to do a quick activity on the child's bed before turning the lights out. This way a child has a natural incentive to get into bed so that he/she can play the fun activity (like a card game) with you. (I write more about these techniques, including what I mean by the technique called "emotional distraction" in other blog posts and in my manual.)
In my blog post on July 3rd, I explained that traditional rewards and consequences often do not work well for extreme anger, because the anger occurs so quickly for children prone to anger overload, and they do not think rationally about earning incentives once they get mad.
In the second half of my parent's manual I explain how you can teach your child to think about other points of view (that are different than her own), and also teach her compromise techniques. But first it's best to lower the frequency of outbursts by using the approaches, like "changing the sequence" and "emotional distraction", that I explain in the first half of the manual.
If you do not make any headway after a few months, then you might want to consult with a mental health professional who works with families of children with anger issues. There may be something else going on in addition to anger overload that would need to be addressed. You mention the ADHD diagnosis and learning issues. These may contribute to frustration for your child; her anger episodes may decrease once reading and writing get easier for her.
All the best, Dr. Dave Gottlieb