So this is the splash page of the extra comic I'm working on!
This is Rue as a teenager (13-14 years). As you can see she is wearing Mari's attire plus a cape to cover her severed arm.
Her hairstyle is based on Kris from the Pokemon Crystal game and she had braces which implies that as a child she did have Mari's overbite. A lot of people tell me that Rue looks nothing like Mari but as a kid they were very similar in terms of height and some characteristics. Mari just has her father's color palette.
EDIT: Fixed her hand (kinda).
EDIT 2: Followed the excellent advice from Goddess Chachi and MyTriforce. While I couldn't change the anatomy much I made a bigger contrast and made her small more proportionate!