How to restore/stretch out a rayon material shirt?

Soooooooooo I bought this shirt from forever21. It is 100% rayon, one of those slightly oversized ones that are in style now (kind of brings a pancho to mind)---it cinches around the waist & then flows down to the hips. Well, my mom didn't follow the washing instructions (hand wash; lay flat to dry)---she put it in the machine & dryer. IT SHRUNK significantly. How can I get it stretched back out to its normal size ???? Please help!