Hello Gill,
My experience is much different from your daughter's, but I will share it with you. I had a colloid cyst of the third ventricle blocking my csf flow creating hydrocephalus, and causing excruciating headaches. In 1994, I travelled from Louisville, Kentucky to Santiago, Chile, an 18 hour plane flight. Once I arrived in Santiago, I was somewhat disoriented for a couple of days. At the time, I was not aware that I had the cyst, or the beginnings of hydro. I felt very dizzy, and brushed it off as "jet lag". After sleep and re-hydrating, the headaches seemed to go away. In Nov 2000, I had a craniotomy and resection of the colloid cyst. It took a while to recover, but I did gradually. In 2005, I flew to Oahu, Hawaii, another 18 hours, and was quite conserned with the affects of cabin pressure on my post craniotomy brain. Besides feeling the pressure from the plane taking off and landing, I did not have any ill affects during this flight, or have the jet-lag I felt in 1994. (granted 1994 was a military plane flight, and I think we flew at a much higher altitude)

I have heard that chewing helps with pressure, ear, and sinus, when in a plane. Does your daughter use a pacifier, or a bottle? Something like this may help as your plane exits the runway.

I hope this helps you some. Please hold on for more experienced people to post suggestions. Wishing you the best, Dodi