I don't have much love for Sansa either, but to blame her for these things is too one-sided. There is a section of ASOIAF fandom that wants her to be a perfect angel who never makes any mistakes and is always right, but even though I disagree with them I understand some of their arguments.

• She didn't side with anyone, she was an eleven year old put into an impossible position where she had to choose between vouching for her betrothed, the future king of Westeros, or her sister, whose wild antics Sansa did not admire and still said she couldn't remember because she still didn't want to side against Arya even though it was her "duty" to lie for Joffrey.
• When her and Arya argue like the children they are, Sansa tells Arya that she'll have to call her "Your Grace," and bow because she is sick of hearing Arya talk about how terrible Joffrey is. Yes, Arya's ultimately right, but Sansa was betrothed and thought that since her parents agreed, and the guy looked the part, he would be a perfect prince and king, and make her the queen, her ultimate dream. It's still the most childish argument ever and Sansa would have never abused Arya if she had actually become Queen and the Wot5K hadn't happened. It's a defense mechanism, not constant bragging. These are little kids saying "When I'm rich I won't give you any money," and siblings tend to, especially ones with different personalities, argue all the time when they're young. I know I did.
• Cersei blames Sansa for revealing Ned's plans so she can make her feel guilty about her father's death. All she did was tell Cersei that Ned was sending them away. Ned's the guy who confronted her in the godswood about everything and didn't accept Renly's offer of alliance. His belief that Cersei would act in accordance of honor the same way he would have is what got the entire household and himself killed. It also led to Sansa's "imprisonment" as a hostage of the Crown.
• If she didn't send that letter she would have been beaten until she did, Cersei was manipulating everything at this point
• Sansa's never safe, she has no options, and then Littlefinger kidnaps her under false pretense of taking her "home" and takes her to the Vale. She has literally no one she could speak to in order to get out from under his thumb, the closest help she receives comes from Lothor Brune and he's directly working for LF. Everyone in the Vale either works for LF or does not know she is Sansa Stark, and she has no way to convince the Lords and Lady of the Vale that she is Sansa even if she wanted to. She is still married to Tyrion and considered an enemy of the crown. Under constant observation and manipulation by a man who has brought the kingdom to war by sprinkling a few lies where they would do the most damage.
• And very importantly, Sansa doesn't know what happened with Jeyne Poole, and even mentions her in this recent POV chapter. When shit first went down and Jeyne was crying constantly, Sansa mentioned this to Cersei so she could go back and allay Jeyne's fear, but Cersei was the one who then took her from Sansa's room and gave her away to LF. When Sansa finds out what happened to her best friend, there will be blood.

Sorry, didn't mean for the post to be long, and I don't mean to get into a heated argument at all, but I used to think along the same general lines and after reading post after post praising Sansa to the heavens, I finally decided that she shouldn't be blamed for trying to do what she was taught as her "duty" to her future husband, and that Ned is the reason Ned died, due to his poor reaction to LF's and Cersei's machinations combined with Robert's death.

I realize this most likely won't change your mind at all, and again, not trying to get into an online shouting match. I think it's valuable to try to see things from her POV, and that the things mostly attributed to her are not her fault at all. She's still a child, with no agency, and has never had the influence to do what you suggest. Sansa was a simpering teenager who is annoying in aGoT because she idealized what she heard, and she paid the price and learned a very hard lesson in the truth of chivalry. Almost all of her decisions are made to protect herself and avoid conflict, and I think most people would react the same way in her shoes. And she still gets a few jabs in at Joffrey along the way.

I don't love Sansa like tumblr does, but I can understand her motivations and decisions. And this post is not meant to discredit you at all, it's to encourage a rethinking of her character in a different context. It's more of a general refute of the basic arguments made against her character. She's really not evil, and is only adapting to survive.

TLDR: She's not evil, I swear! If she does eventually side with LF after finding out the extent of his betrayal, then I'll agree she's become completely immoral, but it's unfair to judge her for other people's mistakes and for trying to stay alive. Sorry this is so long, but if you decide she's not as responsible as you first claimed, it's worth it. Again, not trying to fight or argue with you, just counterpoints to your points because they are common arguments even though they are unfair and untrue.