First, Bog- I volunteer a lot. I volunteered before I got paid to coach, and I volunteer even after my regular working hours. We do exist, and we do it out of love for the sport and the success of those we coach.
Second - we are only getting one side of a story, and we also need to consider many other aspects of the story. I leave kids to work on things independently all the time. Sometimes, an hour is needed to feel out what they are doing, and put it all together. That little bit of push goes a long way. We also don't know how many other athletes are in the gym, or how many coaches. If I am all alone, and it was expected that someone do a skill - they are expected to do it. I teach progressions for a reason, and it's not because it's easier for me. She needs to take it upon herself to do the drills that helped her in the first place, and do them! 3 hours is plenty of time to figure it out.
I know I'm gonna get hated for this, and I know it may be percieved as a "bad reflection" on me, but here goes - your child is in a sport based solely on someone's aestetic and personal tastes. They are bombarded with people looking at them, judging them, telling them everything they do wrong instead of right... kids need to learn to take punches, especially in a sport like this. It is a life skill, if you ask me. If they can't do a skill they have been performing for a year, under a little pressure from their coach - how are they going to do it with a lot of pressure with thousands of eyes watching them? How will they overcome fear at their frist job interview and the interviewer makes them uncomfortable or asks questions that they felt unprepared for? I appreciate the straight forwardness of my coaches, and I appreciate how hard it was. I didn't mind being left alone or "ignored" because I got the chance to move myself forward, and I draw upon a lot of those skills now.
Am I defending the coach? A little. I personally try to encourage growth through success. It's not always possible.
Some athletes, however, need some added pressure - that sense of "I NEED TO DO THIS!" In fact, I would argue that all serious gymnasts, who plan to compete over a long period of time, NEED this.
It's one thing if the coach put some mats on a beam, said "do a flip flop" for the first time, and just walked away. Im assuming there was development, drills, and lead up to this point. The coach is doing what they know how to do to mentally prepare the child. It may have been how they were taught, it may be the way they were raised - whatever it is, it is their method.
You have the right to leave if you don't agree with it. By all means, speak up and say something if you don't like it. But don't be suprised when nothing changes.
What it comes down to - if your child wants to continue, they will find a way to cope and succeed. If there is no physical abuse going on, I see nothing wrong with a little verbal assault (within reason - you didn't say how they were being insulted. If a string of foul words rang across the gym, it's one thing - but if it's "you expect to be level 6 AA champ not doing a BWO? I guess not..." *shrug*)
Life is full of hard knocks. Get back up.