I am not saying that she was or that it has any bearing on the case but theoretically children with developmental difficulties may be more at risk to be harmed by the people close to them or to wind up dead in accidents, possibly after neglect. They also might be more vulnerable to stranger danger in certain circumstances but it may not apply in this case since any toddlers sleeping in their beds are pretty much equally defenseless and unless it was someone who had watched the family for some time a stranger wouldn't be able to tell which sleeping children are autistic or not.
Autism might have a bearing on what happens to a child after the abduction, say, if the child is taken by a childless couple who find her too hard to handle and can't seek professional help for obvious reasons, or if the abductor finds the child's disability a bonus because there are difficulties in communicating her plight to others etc. .
But obviously if she wasn't autistic it's not relevant in any manner so the theoretical possibilities leave us at the starting point.
So the parents left her....LEFT HER....no matter what after.....they left her?! AND younger ones?!!!!