If she flies the only way she can use it is if she checks her bag. Other wise ( as stated in previous post ) it has to be in a 1 quart see - through zip lock bag.
If you are looking for something fast and easy for use in her checked bag. Why not just take a nice decorative handtowel sew a zipper on the top edges and then sew up the side seams. If you wanted you could sew plastic to the towel prior to the other sewing . The best part about a hand towel is they come finished on the edges and there is some with really nice embroidery.