DD is also first year 12u, wasn't quite as petite as yours, but a Louisville Slugger Xeno in 33" mitt works great for her. She was probably 4'10", 90-100 at the time she first got it. Lightweight and easy to break in. Now because of that you can tell it isn't a glove that will last forever. I notice when she's catching for faster pitchers (low 50s), her glove seems to whip around a bit, but I don't know enough to say if it's because it's a lightweight glove or if it's her receiving technique. I got her a liberty advanced 33", but she's been resistant to use it, finding it to be more relatively stiff.