I'm not familiar with anything past the first book, but it seems to me that people forget that Sansa is only a young girl. She's what, ten in the book? She might remain naive and disconnected from reality for the rest of the series, for all I know, but right now I view her actions through the lens of her being young and overly idealistic.

As far as her becoming a leader, I can see her becoming like Cersei later on, figuring out how to use her sex to get into a position of power.