Thank you.

Like majority of things I make it just start by a spark of inspiration and motivation by your wonderful picture and from that ideas was flying off based on the movie, past what ifs in my head, and other factors. I just basically wrote down the flickering random ideas and changed around as I wrote.



Taking now a little more research into the Star Wars lore I can see one problem with Anna being a Sith lord based on what I wrote. If the magic that transformed her into a frozen hearted amorality and unfeeling that could at first present a problem. In Star Wars lore the "dark side of the force" is linked towards negative emotions (fear (thus the reason the Sith though Elsa could of been a strong ally but inside Elsa turn away from them and after the whole event she turned to only anti dark emotions), anger, hated, aggression). The light side was used for defensive reasons while the dark side was used for offensive. If Anna is transformed to be cold and unfeeling than the dark side that the Sith weaponized would be closed off from her. Darth Vader was considered one of the most powerful Sith lords not just due to great training from Anakin and Darth Sidious, natural talents and force sensitive born being, but also because he used hate and anger to fuel his dark force powers. The one he hated the most...himself.



Thus she is either:

A: Isn't emotionless but loses her ability to love and becomes amoral psychopath unable to have a consciousness and have that understanding of good and evil one can feel inside messing with her level of thought and reasoning. No feelings of empathy or guilt in her actions or joy when carried out but lack of understanding moral situations and can only gain knowledge of what is good and evil from a outside perspective take of it told to her. Losing love for others and having only basic animal instinct of self preservation.



B: Total frozen blocked emotions but doing so locks her out of the dark side and possibly light side of the force that relied on emotions however for story reasons have her gain access to another side of the force that was now possible because she is emotionless gaining access to a deeper core within the force and can tamper with it to her whim gaining unnatural abilities.



Darth Sidious desire for power but inherent fear of Force-users particularly ones he was not certain to what they were capable of made Anna's new abilities a desire for him to make Anna his latest puppet yet she terrified him more then any force user had done before for not knowing what she was capable of. What does one desire if one doesn't feel want or desire of any kind? What would be Frozen Hearted Anna's goals and how would the Sith influence her to their own goals? Even robots who might be made to be emotionless has a task or goal to achieve when made formed by their programmer or though their programmed logic in time.



For these reasons of storytelling I feel choice A would be better options allowing her to feel emotions but lack a moral core, empathy, or insight to the consciousness that tells us what is good and evil. She can if needed still mimic emotions acting/pretending based from what she knows from past knowledge and from her surroundings of what others are displaying while not understanding why such emotions are being displayed by others unable to emotionally feel their pain and respond in return naturally.



Last idea working in the two of her frozen heart and the emotional state that the frozen magic worked and how the Dark Side worked is that Anna is lock from empathy and love but is forcibly angry, aggressive, and hateful all the time due to it keeping her alive. The flames of hate, rage, and aggression was keeping the magic from spreading transforming her into pure ice and while doing so she is tapping into the heart of the dark side and the corrupting of that part of force. She may not be working however with the Sith but be on her own side a threat to all. The flames of hate are powerful but while it holds back the ice it doesn't melt it and only the passion of love act of true love can set her free. That with all things frozen inside her a small part remains and Elsa is the only one who can get close to her to free it. That or when Elsa is in great danger and hate isn't the answer Anna let's go of hate and and dark side power but instead accesses that small feeling of love to her sister and her well being which becomes to key to salvation of the sisters.