just as a double amputee is not expected to win a marathon,
I was once a competitive distance runner. I was generally on the left side of the finishing time distribution. Events with a relatively flat course almost always had (presumably still have) a wheelchair division. Mountainous courses did not. I wonder why ...
it is stupid to prevent him or her from participating.
Stupid? Not necessarily. Safety and space limitations, for example might necessitate excluding less capable athletes. Some of the bigger races had (have?) qualifying times. I perceive that you are a Marine. Congratulations: you completed Boot Camp. Not everybody does. There are basic qualifications even to get in. Not everybody meets those qualifications. Would it be stupid to prevent your hypothetical double amputee from enlisting?
We are talking about a LITTLE GIRLS DANCE CLASS here; not some body in a wheelchair trying to run a rough mountain marathon course. I doubt even the new tracked chairs could safely or competently run a mountain course.
We are also NOT talking about a little girl jumping out of a perfectly good aircraft to perform a vertical envelopment operation, it’s a little girls dance class. I say let her try and have some fun; if she can’t keep up, so be it.
She should not be denied the opportunity to try.