YOu might consider making it more like an oversized table runner. Given the narrow airline seats, there may not be much room for her to put a lot of quilt around her...the extra length can be used to tuck under her feet to keep them warm. This style lap quilt is made for folks in wheel chairs and the bottom actually has a pocket to put the feet in. If you need dimensions for something like this google wheelchair quilts or blankets.
And I hope she enjoys Alaska - the trees and flowers are amazing this year.