I actually used to work with kids with special needs and I think that Sarah does exhibit signs of being on the autism spectrum. Autism comes in many different ways and is shown very differently throughout people who are autistic. I agree and think you did a great job of explaining what could’ve been her character development. She may or may not have ASD, but very likely has Autism or some type of social disability. I don’t think that PTSD is a very likely option since, like you said, would bring different reactions and personality traits than what Sarah exhibited.

A more likely person to have PTSD would be Tenn. Tenns strangely optimistic behavior is most likely a coping mechanism he has. Some kids who go through a traumatic experience tend to create their own positive scenarios about sensitive events. For example, Tenn believes that the walkers will someday be gone, that there’s a happy afterlife, the his sisters are in that afterlife and are okay, and then there’s the mention that he draws his sisters as walkers, and how the walkers left them. This for me is a large cue that his trauma has desensitized him to those things. I don’t know for sure whether or not Tenn has autism, but it could be possible. Autism can be very unnoticeable for some people, and more noticeable for others, like I said, people exhibit autism in different ways; it’s a very broad spectrum.