For a time my little girl was about as tall as my shirts were long. So we jumped on sewing for her.
I am just posting this to inspire you. I didn't take pics of the step by step.
Basically, I cut the neck off. folded it under and sewed. I created the basic shape from another one of her dresses and made the arm holes.
You can see I ran out of material so I used a sleeve and turned it the other way for contrast. I added the belt with a simple rose to mimic the added hem.