Sorry to hear your daughter is going through this. You have gotten some great feedback. I’ll just add couple extra thoughts.
At the core of it, she has an interfering thought/belief that is causing a response, creating emotions and feelings, that are impacting her actions. She is still the amazing athlete that was throwing back tucks a while back. She is not broken or abnormal. She has simply developed a belief that is not working for her the way she needs. Actually a pretty common thing. Fear is most likely at the root of it. Could be fear of injury, fear of embarrassment, fear of failing, etc. The problem is that it becomes an automatic response. And many times the athlete doesn't know where it is coming from or how it started. That is why it can be difficult to just practice and ‘work through’ tumbling blocks.
It is difficult to talk specifics, since interferences can be as unique as the athletes themselves, but here are a few general tips that you are welcome to share with her. Might help some.
1) Check internal dialogue. If you are consistently thinking or speaking negatively, that has an impact on your beliefs, and therefore your feelings and actions. When you catch yourself saying something that isn’t positive or resourceful, stop and tell yourself the opposite. Constantly tell yourself the story that works for you.
2) Mentally practice the move. Imagine perfectly doing it. Really put yourself there, feeling confident, powerful, smooth, all the things you need to feel. Be detailed. Rehearse it over and over in your mind for 1 min, several times throughout each day.
3) Before approaching a routine or the skill move, get present. Take some deep, controlled breaths and bring yourself to the here/now by focusing on your 5 senses. Don’t think about the past, or the upcoming routine. Just be present for a moment. A great technique to include with this is to make a short list of things you really love about gymnastics. Things that have nothing to do with the score or outcome, just details of what you enjoy about it. That gives something powerful and positive to focus on, and can help with naturally trusting your skills.
It will be a big shift if she can believe in her ability to change. Overall, it is just gymnastics and not the end of the world

But, overcoming things like this can be a huge win for building overall self-confidence, determination, and resilience. If she really wants to beat this, she can do it! Hope all the best for her and for you!!