Though it's a personal preference of mine to not use an outside trainer for my own horses, I wouldn't jump right to condemning her and saying "I'd never take my horse to her just because she's young".
I, like many others, started training for other folks when I was younger than her. Granted, I generally didn't ride anything too nasty and I didn't have the knowledge to do all the finishing work that I can do now, but I could turn out a sane mount that just about anyone could ride if they didn't need anything fancy. For most riders, that's just about what they need...a horse that they can catch out of the pasture, put their saddle on, mount up, and ride off without having to worry about getting kicked, bucked off, run off with, run over, etc.
Just, for example, this mare. She was one of the first "green" horses I ever worked. My Dad had put a handful of rides on her before he just handed me the reins and said "she's all yours". She would go, stop, and turn (most the time) when I started riding her. By the time she went home, I was loping circles, she'd seen about a million miles of trails, she'd been roped off of, and you can see she'd ride bareback...all with a calm demeaner and a level topline. I was about 12-13 at the time.