I think there's an aspect of right and wrong here.
Dd2 is missing her hand and authors generally are completely off. Usually the character is either a sympathetic disabled child who is there to show the main character's caring side (or the baddy's nasty side) or their character is all about the disability.
Her life is neither. There's times it effects her, both positively and negatively, but most of the time it's there. It makes a difference that she turns to pick it up in her right hand, or maybe she can't carry as much, or she tucks more things under her arm (chocolate biscuits were interesting when younger), but those are small things. It doesn't define her as a character or make her weak and grateful that the main character speaks to her etc.
I think when you're writing about a minority character that you are not directly experienced with, the temptation is to make it too big a part of their life. So you want to shove in all the examples you've been told by people who have experienced it. And show how unfair it is-it can become a crusade.
But making it obvious without shoving it in the reader's face is difficult. I've tried writing what dd2 would like and there's such a small line between enough mentions that the reader doesn't get a shock every time it's mentioned and think "oh that's not my view of her" and so many it's being rubbed in the face the whole time.
Going onto the other side, authors do write convincingly about things they haven't directly experienced. I don't imagine Lewis Carol ever fell down a rabbit hole, nor C S Lewis found a new world at the back of a wardrobe.
If we say we can only write about who we are, we're stilting the potential literature into only having writers types as main characters.
And I have every faith that Anthony Horowitz would manage it excellently. I assume he's never been a teenage spy? Or a Russian Assassin either? 
Or maybe he'd like to admit to these? I think we'd all agree he's created realistic characters there.
He does plentiful research into his subjects-he's not going to produce a cardboard stereotype. I'm sure he'd take advice from people who have experienced it directly and edit accordingly.