Enlarging the Brunch Jacket from size 8 to size 10/12

My DGD wears a size 12 (I think). I’ve taken her measurements and the’re all over the map, but definitely larger than a size 8. She’s nine years old, thin and tall. Her measurements are chest: 26”, waist: 22.75”, hips: 29” and BW: 13”. She is 56” tall. Her arm length is 19”! In other words, she is all arms and legs! If anyone can give me some guidance on how much and where to add for her, I’d be very grateful. Obviously, I’ll have to start by adding length; that’s not the main problem. The main issue is where to add width. I’m thinking she will need extra in the armhole length, maybe 3/8” as well as in the back length, extra width in the sleeve, a larger neckline (and facing), etc. TIA.