This requires sewing https://www.youtube.com/watch?v=du1G576lRzE"]https://www.youtube.com/watch?v=du1G576lRzE
I do work for a lady that has a tshirt line and she is always complaining about how hard it is to find a tshirt to fit larger women without being boxy. I will have to pass this on and see if she would be into just resizing...she wanted custom t's made from scratch but with this method she could buy her usual batches and just resize a few...veddy interesting!
The catch 22 about using this method for bigger girls is the shape variable. Depending on dimensions, a good fit may come from radically different base shirts for several women all of the same tee size. Also, you may want to get a ball point needle for sewing knits to prevent runs. Tissue paper or fusible web can also give you a smother finished seam and prevent machine jams, and some knits NEED a zigzag finish to prevent runs.