Totally normal, but no fast fixes.
First, a metaphor to help understand the effects of a growth spurt in gymnastics:
Imagine you spend 10ish years driving a small, sporty little 2-door car. A Miata, or something like that. Over time, precise control of that car becomes second nature. You know exactly how hard to push the brakes to stop in a given distance, exactly how hard to push the gas to get the accelleration you want, exactly how far to turn the wheel to get around any given corner, exactly how big a gap you need to get through in tight traffic or a parking lot, etc. You can probably feel roughly how fast the car is going without even checking the speedometer, because you know what it feels and sounds like when you're driving the proper speed for whatever roads you typically drive on. Complex driving maneuvers like parallel parking or backing into a small space or navigating a mall parking lot in December are all relatively easy, because your brain has built up this subconscious encyclopedia of precisely how that car will handle.
Then, imagine you switch to giant SUV or pickup truck or whatever. Now, at a surface level, your truck works exactly the same as your tiny coupe. It still has a gas pedal that makes it go, a brake that makes it stop, and a wheel that makes it turn. And yet, that whole encyclopedia you had for how to control your car has to be rebuilt from scratch. It has a different turning radius, a different mass, takes up a different amount of space, and just overall handles very differently. More complex maneuvers in tight traffic are now a lot harder and a lot scarier than they were before.
This is what your daughter is going through with her body right now. She has built up a subconscious encyclopedia of exactly how hard each muscle has to work for a given skill, exactly how fast each skill should happen, the exact timing and angles and balance and so on.... and suddenly that entire encyclopedia is irrelevant, and has to be rebuilt from scratch.
Growth spurts tend to have a more dramatic effect on bars than on other events, and especially on cast handstands. Cast handstands are, on a basic instinctive level, scary as all hell. You have to lean headfirst forward over the bar with nothing below to catch you. Not all that hard to gradually build up a level of confidence in finding exactly the right balance and angles and so on, but when all that suddenly changes, the brain (quite reasonably) does not want to let the body aggressively lean forward over the bar, because it no longer feels stable and controlled. In addition, the longer limbs mean the muscles have to work much harder, and the timing is suddenly different as well.
The solution is to relax as best she can and just keep grinding. This is normal. Frustrating, I know, but normal. In time, her growth will slow, and her brain will be able to rebuild that encyclopedia of micro adjustments that work for her body's new dimensions. She doesn't need to consciously or deliberately do anything; she just needs to keep doing gymnastics. The rebuilding of confidence and knowledge of the microadjustments that work for her body is a passive process; her brain will do it over time just by staying in the gym and continuing to do things. There's no way to rush this process; it's just a grind that comes with the territory of doing gymnastics through a growth spurt.
Try not to stress about it. She'll have a rough season while she's growing; everybody has those. If she sticks with gymnastics, the skills and confidence will come back in time.
