Here’s a snip from the new TV Guide that talks about Sansa’s path in Season 5. Mild spoilers

The Vale: Sansa Goes to the Dark Side
The writing takes a daring turn this year when the tale of Jon’s half sister, Sansa Stark (Sophie Turner), goes beyond what happens in Martin’s books. Last season, the once-timid girl, who had been married off to Tyrion, escaped King’s Landing with the help of Westeros’s own Frank Underwood, political operator Petyr Baelish, aka Littlefinger (Aidan Gillen). The unlikely duo took refuge in her Aunt Lysa’s (Kate Dickie) home in the Vale of Arryn. Along the way, Sansa learned Littlefinger had helped orchestrate Joffrey’s death. Her middle-aged guardian planted a creepy kiss on her and later killed Lysa to save Sansa’s life. By the season finale, Sansa had transformed into a raven-haired, black-clad strategist prepared to play the game and help Littlefinger in his master plan to control the kingdom.

“She’s been an observer of tragedy her whole life,” Weiss says. “Everything she’s seen has been a horrible, teachable moment. And now she’s ready to unleash what she’s learned.”

Source: TV Guide