No, I don’t think a character like that is offensive. However, is she making those characteristics the center of the story? I would be very offended if there is nothing about the character except he is autistic, effeminate, tomgirlish and androgynous. I want to see him as a human being with fleshed out human being’s characteristics, not a caricature of a stereotyped autistic person.

It would depend on how they are portrayed. If the writer has no personal knowledge of people with those characteristics and makes generalizations about autism or gender fluidity that seem inauthenitc, it could be offensive. “Write what you know” is the first dictum of writing.

Autism is in infinite depths and individual experiences. One thing which is broadly observed is autism makes the person highly sensitive to various stimuli. This gives some people the impression that boys are feminine.
I have a family member who is autistic. He seemed fragile during his youth, but he enjoyed sports and is very good in a variety of sports. He is all man, but he is quite sensitive in some areas. Fortunately he is capable of communicating his feelings. Fabrics and clothing labels are a big issue for him. Texture plays a role in what foods he will eat. At first meeting, some might consider him feminine, but he certainly is not.
Some autistic persons don’t communicate well. With them, it is much more difficult to determine just how they feel. A boy might want to wear a dress, but it might be because he feels feminine, or it might be he is more comfortable with the loose fit and fabric too might be a factor.
People are individuals, and that includes autistic people.
There are many who are educated in groups, so they know other autistic people. If your friend is concerned about how people might judge her by the way she presents her character, she might want to include other characters who are friends. That way, each would have different personalities. Then it could be seen that only one of her characters is presented as such.

i dont see anything wrong with it. also i dont have much to say because @Patty_Melt already covered almost everything i was about to go over.