Re: how would you respond to this question?
I would say.
"I'm sure you meant to say..'why is she in a wheel chair'..?"
They will feel incredibly stupid, stammer, and say "yes".
Then you can explain if you want. But if they are rude, you don't have to say anything at all. An 11 year old knows better than to ask such a stupid question.
But for the rude people I would (because I am a sarcastic witch) I would say "Nothing, what's wrong with you?"
You Do have to be careful though. One morning at the dance rehersal, I asked a little girl if she was six. She was missing front teeth. BUT, she was extremely tiny. She said, "Six and a half". I said "I miss when my daughter was little" I did not mean it to be an insult. But they were all so cute. Her Mother became absolutley RUDE to me/in front of me. She VERY loudly told her daughter that "You don't owe nosey people an explanation about why you are small" (WTF??) I was referring the the whole class. They were cute! What was wrong with pointing out how cute and little they were?