Mary-
Wow - nice work! May I suggest not shipping it - just keep it for yourself??? No? Okay, that was just a gut-reaction suggestion.
Here's how I shipped very wet oil paintings when I was working as an illustrator. [*Note: the very fact that I had to do this shows my innate ability to get work in at the last possible minute. Oh yeah..
and I learned how to run down a speeding FedEx truck.]
Get a hold of some 1/2" thick Fomecore and cut two large pieces about 2" bigger than your artwork. Using china tape or some other low-tack tape, affix the work to one piece of board, leaving an even border.
Next, cut some 2" strips of Fomecore to create a "frame" around the piece, taping the strips to the border area.
Then, take the second large piece of Fomecore and place it on top of your "frame." Affix 4 pieces of tape to the top and over the back of the 3 layers of Fomecore, creating a top-hinge. At the bottom, use 2 long-ish pieces of tape and do the same, except fold the ends of the tape over, so you can use them like pull-tabs.
Take this whole thing and wrap it in bubble-wrap. If you can score some cardboard corners (or you could just make some), tape those to the corners of the bubble wrapped package. Slide the whole deal into a cardboard box, stuff any excess space with paper, add the invoice and ship it!
Oh, on the off chance that someone might pay attention to this, write "FRAGILE: GLASS" all over the box. Writing something like "DANGER: TARANTULAS" usually puts up a red flag. Plus, your client won't open it, I suspect.
Best,
Rob