This book is not an attempt to teach children about disabilities. The person just happens to have special needs and is part of the ordinary world in which the main character lives. She showed up in the story when I was writing the first draft without being part of my original plan, but turned out to play an important part in the plot.
In my opinion it would be a good idea for more fiction books to include people with special needs without portraying them as pitiful. Perhaps that would help eliminate some of the prejudice that still lingers in our society.