PCSLearner,
It sounds like the only think left for your daughter to learn is that head aches are inevitable, just like her cycle. As she learns the self discipline to deal with these head aches without needing your direction, she will become able to endure them with less anxiety. Anxiety is the worst thing for a PCS head ache.

If she gets to the pint of saying, " I feel a head ache coming on. I need to stop doing this and take a break," she will have crossed a major hurdle. Her school should provide her access to a lounge where she can get a quiet break when she needs one. This self-regulation will free her from much of the anxiety.

We (my wife and I) have learned that there is rarely anything happening that is so important that I cannot take a break.

Others have talked about neuro-feedback but simple bio-feedback where she learns to lower her pulse and blood pressure might be helpful. She can even try this on her own. All she would need is a blood pressure monitor.

They cost about $30 or a bit more. Some will fit on your wrist and can be worn throughout the day. She would just need to activate it when she feels like she is getting overstimulated and then focus on relaxing her body.

Sounds like you are doing a lot of things right. Most of PCS recovery is common sense. The younger ones just need some reinforcement of good discipline.