There’s always a pattern. It’s never random. Sansa’s hair is constantly reflecting the people she’s learning from, or mimicking, or inspired by at the time. In the world of Game of Thrones, even a spec of dust has a meaning, so when it is something as major as a hairdo, you know fans will be inspecting each detail with a fine-toothed comb. The way the characters wear their hair, their dresses, their accessories, there’s always a reason for it.
Even Sophia Turner, who play on-screen Sansa said in an interview, that it’s no coincidence.
When she’s Cersei’s prisoner, and she’s kind of absorbing all her manipulative techniques, it’s reflected in her hairstyle.