I think this will get to you much after Christmas...! Sorry about that.
To mail a pastel I suggest you mat it leaving space between artwork and mat, and enclose it between two pieces of corrugated cardboard. Wrap it with wrapping paper, secure with masking tape, and.... affix postage and address.
As long as the pastel surface is not touched by anything it should be ok. That's why I said to leave space between pastel and matboard. You can do that by securing strips of foamboard between the pastel and the mat.
Hope this helps even if it's a bit...late!!:)

Rita