Time travel can make Sansa more confident. When she travels back, she has the knowledge of future events. So she can be more assertive. For example, she won't be as easily manipulated as she was before. She becomes a stronger character as she tries to change the fate of her family.
In some fanfictions, Sansa travels back to a time when she first meets Joffrey. She then uses her new - found time - traveling wisdom to avoid getting engaged to him. She could instead manipulate the situation to get betrothed to someone more favorable to her family. This would completely change the course of events, not only for herself but also for the whole Stark family and the Seven Kingdoms.
Another theme is the power of knowledge. Since she has knowledge from the future, she uses it to her advantage in the past. This could be knowing about political plots or the true nature of certain characters. For instance, she could expose Littlefinger's schemes much earlier. It's about how this knowledge shapes her actions and the events in the past.
Another great one is 'Back to the Beginning: Sansa's Time Travel'. In this fanfiction, Sansa time travels and finds herself in a position to rewrite history. The author does an excellent job of weaving in the politics and relationships from the original story, making it a fascinating read with a lot of twists and turns.
Their relationship might become stronger. Through time travel, they would face many new and dangerous situations together. For example, if they travel to a time when the White Walkers first invaded, they would have to rely on each other for survival. This shared experience of fighting for their lives would deepen their bond. They would also have more opportunities to understand each other's perspectives. Sansa might see Jon's leadership skills in different historical situations, and Jon would see Sansa's political acumen in various courts they visit during time travel.
Sansa would be more assertive in her political moves. She has seen the consequences of inaction and bad decisions in the future. So, she would be quicker to make decisions that benefit her family and herself. For example, she might be more involved in military strategies to protect the North.
One plot idea could be that Jon and Sansa travel back to the time before their family's downfall. They could use their knowledge of future events to prevent Ned Stark's execution. For example, they might be able to expose Littlefinger's schemes earlier. Another idea is that they travel to a future time where the White Walkers have been defeated, but they find new threats emerging and have to figure out how to deal with them. They could also travel to different kingdoms in different eras and learn about different cultures and forms of governance, which could then help them better rule Winterfell and the North.
In 'dark Sansa Stark fanfiction', Sansa can be more assertive. Unlike in the original where she is often a victim of circumstance, here she takes charge. For instance, she might not wait for others to rescue her but actively plot her own escape and revenge.
She would become more confident earlier. Instead of being a naive girl in King's Landing, she'd use her time - travel knowledge to be assertive. For example, she'd not be easily manipulated by Cersei.
Another theme is self - discovery. By traveling through time, Sansa gets to see different versions of herself and learn more about her own strength and capabilities. She might realize she was stronger than she thought in the past or find new skills in different time periods.