Thank you BlaiBob and Iwannacaoch!
She isn't a rec kid, she's a level B (pretty much like level 3 in US) and has all the other skills but this to move up to the next level. I wouldn't say it's her shoulder strength, because she can do almost 10 chin ups, a great back extension roll, a kip etc. There's many kids much weaker in this group who can FHS. She just doesn't get this skill. I think it is her mind model of the skill like IWC said. How can I change it?
If she wasn't part of a big group I wouldn't made her do the skill by herself for a little while but she has to because we don't have many spotters and we have to have some stations they do by themselves. When I spot her I push her shoulders to the opposite direction and that usually causes a pretty nice try with straight knees. I have even taught other kids to place their hands on her shoulders when she blocks and that helps a little but of course they are kids and usually miss the timing.
She does the same mistakes when we do front handsprings from two feet on tramp. She does ok as long as I only make her do a handstand flat back but.
What drills should I do with her? We do handstand hops every practice. We do handstand forward rolls. We do handstand hops - flat backs. We do them slow motion of a spotting block. We do quick handstand kicking the wall behind. We do handstand holds.
Tell her it's common and admirable for kids to want to do a skill so badly that they spend a lot of time trying to figure out how to do it before they've been given a chance to learn from their coach. Then have her explain the skill to you as if she were the coach and you the student. You want her to do this with no concern for anything you have told her, so have her forget about your corrections and just to focus on what she feels is important. If she won't commit to an explanation of the skill you need to ask her what she believes are the important things she feels she has to do in order to make it from her hands to her feet.
If she still can't explain the skill you can ask her if she thinks it makes sense to reach upward with her head as she leaves her hands. The goal is to get to a point where the two of you are comparing your model to her's to see if there are differences, she believes in, that are conflicting with the proper model. That should give you an pretty good idea of where her problems come from.
When kids have their own version of a skill they will take everything you say and apply it to their model, and that changes your correction as it receives secondary priority in favor of what they believe works. They honestly believe they are doing what you asked, but don't realize they modify your corrections to fit their version of the skill.
For instance.... if you tell her to push her head back as she blocks and reaches though with her feet, she add the correction just before she throws her head the wrong way. You end up with 10% effort on the correction, and 90% effort on the old model. Since it's not enough to work she'll think she needs to do better at applying her model so she can get your correction to work. So go ahead and tell her you believe she's been trying, but that she's been trying to do two versions of the skill at the same time, and that's too much for anyone to be successful with.
Thank her for her efforts and then tell her just one correction to make, and add that her entire existence for that moment is that correction and nothing else matters. Making the skill doesn't matter....... eating, sleeping, breathing, and shelter are nothing compared to the single thing you want her to focus on making happen. Tell her the only way you'll be excited about any progress made on this skill is if the progress comes from the effort you want on that correction, and that even if the skill gets worse you'll be pleased if she makes the correction happen..... even if everything else looks terrible.
That ought to provoke something good.