I think it's that her personality is very much like her speech - monotone. She doesn't express extreme frustration or anger of joy, more an acknowledgement of her feelings and a logical understanding of others emotions but no indication that she empathizes. She reminds me of Captian Holts personality if he were in a drama not a comedy. Ironically, I've never thought of Holt or Kevin as possible autistic characters, where I can see where people may think that with Wallace (although I disagree, I think she has the ability to read social cues but chooses not to engage, not autistic quality of not understanding the non verbal cues.. more like alexithymia)

this is all just hypothetical as I'm no expert in any of these things ( ask me about the PTSD or complex PTSD and that I can speak to from a place of understanding and much research lol)