Hey Yippy,
I'm asking what, not how or whether
Let me explain ... When she asks for the 100th time: "why does my brother do these weird things / why is he like that", we could of course say something like "Because he's autistic. The docs have checked him and that's the reason" - it would probably stop the nagging questions for a little while. But I think we can do better.
Seems to me that sometimes what she means is "his behavior annoys me", in these cases we tend to respond with empathy (yes, it's hard for us too sometimes) followed by small bits of concrete advice on how to get along with him more easily. It seems to work - she's very patient with him. Lately his speech has improved a lot, and I reckon that's mostly her work. She is a real blessing. So I suppose that part is probably covered.
Other times it seems to me that she's basically repeating questions that other kids have asked her about her brother. This part I struggle with. My better half has proposed we just go with "he has communication problems" because it's more descriptive, and actually points towards the idea that others may help him overcome some of his difficulties - as opposed to "he's autistic" which, to her peers at her age is probably just a label that doesn't explain anything. (To be honest, after reading up on autism for the last few months in all sorts of places on the web, it still seems a very ill-defined word to me as well).
Also, "autistic" is occasionally used as an insult around here.
OTOH I have always had a perverse tendency to "wear" potentially insulting labels with pride when I've been called weird, not normal, politically incorrect or whatever. A rather puerile part of me wants to design some kind of "autie pride" t-shirt and get like 10 made for each family member, so we never have to wear anything else again
_________________
Father of 2 children diagnosed with ASD, and 2 more who have not been evaluated.