Heavy metals would probably be to weird for her/?????
ask her about trauma history
whiplash, head trauma, etc
these could be indicators that headaches are not metabolic but mechanical in nature
cranial osteopath or a good manual therapist that does cranial manipulation
or course I always prefer someone who works on everything:
cranium, nerves, vasculature, organs, bones, which in Europe you should have.
If it looks like that is possible and you need a referral I might be able to find you someone if you don't already have one of those in your back pocket.