I'm so sorry that your daughters been experiencing headaches since shes had her gallbladder removed. It sounds to me like she had a reaction to the anesthesia and its built up in her system.
It sounds like shes been to every doctor or done every test to get an answer.
Have you taken her to a Neurologist? Years ago, I was in a car accident and I hit my forehead on the steering wheel and I started having memory issues and headaches. My primary doctor referred me to a Neurologist aand he put me on Topiramate and that helps. I also take Ubrelvy. Ubrelvy tablets are used to treat migraine headaches in adults, that are with or without aura. Ubrelvy works by blocking a protein called CGRP in the nerve endings that are involved in pain and migraines, this helps reduce pain and migraine symptoms. Ubrelvy is from the CGRP inhibitor class of medicines and is a prescription medicine.
My doctor told me I can take it even if I have a bad headache. Luckily, my headaches haven't been bad enough that I had to take any.
It's worth talking to your doctor. This medicine is very expensive.
I hope your daughter starts feeling better.