Good evening,
I would sugget to take your daughter to an O.R.L (ear specialist) motion sickness is often generated from cristals which are part of the ears.
On the other hand I think it is a very good idea to give light sedatives (under doctor's suppervision of course) to small children, being a captain I can assure you that children crying hours is not a prety thing, for the child, parents, and other passengers.
Have a nice flight
