sizing for the dress?

im making a nightgown for a 6 year old, her mom sent me these measurements Head: 21 1/4" Chest: 22" Hips: 23" Shoulders: 26" Bum: 24 1/4" Shoulders to hips: 14" Shoulders to ground: 39" Top of head to ground: 46 1/2" on the size chart it looks like she is a 4 for the hip and chest but a 6 for length (she is a pretty tall skinny girl). I bought the size 5 and up pattern. Can I make the 5 and lengthen it? Will it be too baggy?