This is GoT, not Law and Order...

I don’t think they lied to us. To me the tension between Arya and Sansa seemed real. The point that broke it was when Littlefinger tried to convince Sansa that Arya wanted to be Lady of Winterfell. She knew better. Once she ran that through her head, talked to Arya and Bran, everything came clear.

*Governor Carcetti

R.I.P. Mayor Carcetti.