I don't know how she did it but these are the instructions I saved when I was going to attempt it: Hope this helps
First you will need the dye. I got a kit at Michaels that came with the instructions, dye, squirt bottles, soda ash, gloves, and rubber bands. Get 100% cotton shirts. That is very important so that you get vibrant colors.
Take the shirt and draw a mickey head in pencil, on the shirt. I made a pattern on papper first and then traced along the edge. You will then "sew" the pattern. Use a needle and thread. I got a waxed thread at Michaels to make sure it didn't take up the dye. Sew a 1/4" - 1/2" basting stitch along the pencil line. A basting stitch is a very simple stitch that goes up & down through the fabric. Only go through the front of the shirt if that is where you want the mickey to be. If you want it on front and back. Do each side separtely. After stitching along the complete line, knot it, and pull it tight, so the fabric gathers in a bunch. Make sure the inside of the Mickey is poking outward. Pleat the rest of the fabric, so that you have a long snake like tube. The more careful you are with pleating the fabric along the length of the shirt, the better the final result. Go easy, and take your time. Wrap a rubber band around the threaded bunch. The tighter the tie, the more defined the outline of the mickey will be. Place remaining rubber bands in 1"-2" intervals along the rest of the shirt. It is a little hard to explain, but when you are done you will have a long snake. One end is the mickey on front of shirt and the other end it the back mickey. Through the middle is the rest of shirt (arms, neck etc.).
Then follow the instructions in the kit for preparing and dying shirts. The squirt bottles make it possible to get the specific color where you want it.