It was super easy. I cut up the back of the shirt and took it in, measuring Miss Kinder and being sure not to skimp on pinning. I also cut the seams of the arms and took them in as well. The neck was easy to take in without too much trouble, by pulling the fabric in under the buttons on either side, since the buttons were big enough to cover up my work.
Next time, I want to try one with long sleeves, so I can make the cute leg warmer like Amy Karol did over here on the inspirational angrychicken.