Ok, what the actual? You think your SIX year old is AUTISTIC, which is a disorder which many people (and obviously yourself) do NOT understand because she is being a child and drawing on a wall even though you told her no, and hit her? Really? You seriously jump from "Oh, my child need stimulation and a way to express herself" to "Oh well she must be mental"?
Jesus H Christ on a cracker, Lady I think you might have been huffing a few magic markers. Drawing on a wall is a normal kid experience. All kids do it. And you know what? "I don't know" is a good excuse. She is six years old for crying out loud, its not like she can write a paper and explain the thought process behind it. Kid's simply cannot explain WHY they do certain things. They just do them.
And spanking your child? Gee, way to introduce violence into the household there, Chief.
Look, if autism is a concern, there are markers. Missing major milestones as a infant/toddler for one (by massive amounts, might I add). Social anxiety. It will have had to happen in your family as well, which is referred to as family history.
You can't self diagnose this and phrases like this hurt not only your children but demean those with this actual disability.