M.P.
The answer to this question depends so much on the child's level of understanding and social skills.
It's important to give her as much information as she needs at the moment and as she grows older. Be sure to include values and expectations for her behavior as well as facts.
Just as with "normal" children answer her questions.
My granddaughter is 9 and she's become interested in boys and is telling me what she thinks about hugging and kissing. She nearly always starts or ends the conversation with "I know I'm too young now" and then continues talking. So I just listen thus giving her support for her ideas which are reasonable.
There isn't a time table or a correct way to tell any child about sex. There are some very good books that you can read with her. Then initially answer her questions without detail until she asks another question.
My 6yo grandson is some where on the lower/higher? end of Autism Spectrum Disorder scale. Perhaps he has Asberger's. He's inappropriate with his kisses and his touching of his mother and me. We just keep repeating to him that is not acceptable. It is difficult for him to understand why not. At first I tried to explain about privacy and right to be free of touches. His response was that he drank milk out of them and it was OK then. I stopped trying to help him understand. I say this is not OK. Stop. And he's getting better at not touching. His mother has stopped letting him kiss on the lips because his kisses are sloppy and filled with tongue. That is helping too.
I remember my daughter asking such questions at that age. Being open to questions and answering them simply works best. I think this is true for most kids. When the child is autistic the difficulty may be in getting them to understand the social expectations. Perhaps that is part of your question. I don't know the answer to that.