In general I think I can understand how some people might be uncomfortable with Sansa’s seeming lack of reaction to Rickon’s death, but I think a lot of it is also subjective interpretation. I saw that scene as Sansa barely holding it together, barely containing her emotions, and then later taking out all her pain and anger and grief on the evil man who caused it. She might have done it is a less physically direct or obvious way than Jon, but the emotion was still there to me. I also think that Sansa knew and had, at least somewhat, accepted Rickon’s fate already honestly, so I agree with you there. If anyone knew what Ramsay was capable of doing, it was Sansa.
But yes, I do think a lot people wanted grief and misery inked all over her face and tattooed on her forehead in big black letters. I think many people have developed or accepted ideals about the “right way” for a “good character” to death with grief, and trauma, and pain, and loss. And any character who doesn’t fit into that little box must somehow be wrong or bad, which I find extremely and unnecessarily narrow minded tbh.
Good, compelling, well written fictional characters, while they are not real people, are written as imperfect humans. And there is no “right way” for a human to grieve. Just because Sansa’s reaction didn’t fit into the little narrative box that some people have marked as their “grief and trauma comfort zone” doesn’t make it wrong.