Your daughter's condition, as you've probably been told already, is quite unusual. There are a few things which may help explain some of this, however.
First of all, when a person has an anxiety attack, or even is displaying signs of anxiety even if it is not a full blown anxiety attack, that process causes the pupils to dilate--it is a very basic part of the "flight-or-fight" sympathetic nervous system reaction. Secondly, when a person is in a low-lighting environment, the pupils are automatically going to dilate more just because their job is to let more light in when the ambient lighting is low (to allow for more clear vision) and to constrict, allowing less light in when the ambient lighting condition is bright. So when she is in a dimly-lit environment with her pupils already wider and she sees bright spot lights, this high contrast naturally causes an irritation or to those who are more sensitive to it, like your daughter, can cause symptoms of eye strain and also headache, which may even further exacerbate anxiety issues.
Secondly, those people who get headaches not uncommonly tend to have issues with their eyes, just because the eyes are connected to the brain and are many times an unwilling participant in whatever the brain is experiencing. In other words, it maybe that her headaches are the cause and her eye symptoms are a secondary symptom from the headaches. This is not uncommon at all.
Knowing that she has these issues, I would recommend a few things. First, there may need to be an investigation into headaches and possible treatment trial of different medicines to see if these can help her and to find any possible causes of headaches. Secondly, I don't know if she is on any anti-anxiety medications, but appropriately treating this may also provide her some overall benefit. Lastly, she may be someone who just naturally has larger pupils than others, and it sounds very possible that she is. In that case, you may consider having her use tinted glasses, or sunglasses, or even using a low concentration of a drop called pilocarpine, on a daily basis, that helps to constrict the pupil--this may give her some relief as well.
Does all this make sense? Do you have further questions about what I've said or anything else?
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My opinion is solely informative and does not constitute a formal medical opinion or recommendation. For a formal medical opinion and/or recommendation you must see an eye doctor.