Ok, I may be new here (ig; cheddy.ju) but I just wanted to share why I think that Rina Tennoji is good representation for autistic people (even if she isn't autistic).
Ok, first of all; I'm autistic myself. I was diagnosed some years ago at 13 (late diagnosis), and I heavily love autistic-coded characters (like Hina Hikawa, from Bang Dream!). So yeah, this is my entirely subjective opinion and a headcanon overall.
Then let's get to it; why I find Rina Tennoji is good autistic representation.
To begin, I think that her whole "can't express herself" thing is pretty relatable, but my analysis goes beyond that. Autism is seen in different ways, and this could be just a part of her personality beyond the spectrum.
What really catches my eye is how the girls treat Rina in the anime when she isn't able to express herself: they accept it. There's no punchline involved at Rina's sake. I mean, there's comedy in those moments, but it never is to paint a negative light on Rina. They just kindly laugh it off and continue the conversation.
Another thing that I love, is how the anime portrays the message; "there's nothing wrong with you". In rina's episode, we see how she is trying to change herself to be "normal" (I surely can relate to that), but forced change is never the solution, as the other girls notice. They keep on accepting her, and when she uses another medium of expression (Rina Chan Board) that accomodates her needs, they are happy for her.
And I think that's the great message overall; there's nothing wrong with you. You don't need to change the typical way, and people should adapt to you; not the opposite.
Is Rina autistic? Probably not officially, but it still can be relatable to autistic people like myself, and feel a little bit more represented in media.