Okay, so just as a general statement, a lot of Sansa stans have been or are survivors of abuse or sexual assault, and I think because of how society in general likes to place blame on victims it also contributes to the fandom narrative of Sansa’s perception, and for the most part (of course not all, there are a ton of other aspects to relate to in Sansa’s strength) Sansa’s fans see her strength in how they wish they could have acted in a similar situation or simply just by going through a similar situation.
That being said—
In the show, Sansa is a thirteen-year-old girl who is thrown into the den of lions who are much more politically aware, politically powerful, older, and taken much more seriously than she is. After Ned’s death, she is a commodity. As long as she doesn’t die or loses her maidenhead or gets pregnant, pretty much anything is fair game. So from Ned’s imprisonment on, she’s a pawn, living in a constant state of limbo and fear. Her strength comes from how she’s learned to navigate this situation without breaking and without giving up who she was raised to be or her innate sense of compassion.
At the age of thirteen (show canon), she goes before Joffrey and begs for mercy for her father. She tries to treat with Cersei to stop Robb and, as she’s led to believe, save her family, all the while realizing her future husband is a monster who is inevitably going to abuse her and their children. She is completely and totally alone, and looking forward to only isolation and pain.
In S2, she is physically and emotionally abused. She does not break, she does not flinch, she does not make a single mistake in the presence of her abusers. I know this… isn’t apparent to people who haven’t been in/witnessed abusive relationships, but the pressure she is under is immense. Sansa is walking an extremely fine line—and yet she manages to both A. retain her sense of self and subvert her abusers and B. not anger them further.
When Joffrey sexually assaults her in front of court she does not bow, does not break. She takes Sandor’s cloak, covers herself, and strides out of the hall with her dignity in tact. She does not take Tyrion’s offer out.
She manipulates Joffrey (something Cersei and Tyrion are unable to do) multiple times. She is not afraid to look her jailor in the eye.
After the riot, she doesn’t feel hatred towards the rioters. She still, even after all that has happened to her, doesn’t understand such violence. But she wants to. She feels compassion for these people, said she would have given them bread—she does not resent them, she instead tries to understand their plight. If that’s not strength of heart I don’t know what is—that the Lannisters and courtiers don’t make her give up on humanity.
And then the night of Blackwater, when Cersei abandons them, and Sansa steps into the role of the queen, calming the women. When she kisses Joffrey’s sword, backhandedly insults Tyrion, refuses to flinch before Sandor. Sansa is here to survive, but she is not here to cower. She has backbone like no other. And she is strong.
She is strong without needing to wield a sword or compromise her femininity—things that are her. Sansa loves clothes and hair and courtesy (which is her armor) and people, in general and she doesn’t need to learn to cut someone’s head off for strength. She doesn’t have to be able to fight to have strength, anon. Her strength is all inner, and she becomes strong through horrible tragedy, instead of brittle or mean or apathetic.