OP,
you are being too intense. Yes your DD will likely be not the best dancer in her class or school but so what, it’s a hobby she enjoys, she isn’t dreaming of joining the royal ballet.
Your DD is going to face the situation eventually where another child, or children will be better than her at something. Dance, maths, science,….
Your job is to teach her the difference between valued/good enough and the best/star. Getting the grade on the first try is phenomenal. It’s better than ‘good enough’.
A person can have confidence and feel proud even if they are not the #1 or even top 10 in something.
You need to stop pressuring her- because that is where this anxious concern will lead to. Nothing she does will be good enough unless she is the best and you will push her thinking if she’s at the top, she will be safe from disappointment and envy.
She’s put hours into dancing, she enjoys it, she got the grade celebrate and stop nitpicking her. Think of the grades like belts in martial arts, they don’t do merits or whatever, if you pass the exam you’re a red belt….if you don’t pass the exam, no biggie you keep working and you will eventually pass. Some people just have to work harder than others at something. There will be kids who have to work harder than your DD to get to the same grade she is at. That’s life, we all have things that are easy for us and hard for us.
This is what she needs to learn.