Maybe Jaqen's trial to Arya is her giving up own life? Either that, or it's just based on that whole philosophy that there are no good/bad events and it's the ego that's attached to everything giving meaning to everything that's all in her head. She can't beat the other girl because she has not fully let go and come to accept what happens, happens. The fact that she cares about beating the other girl so much shows that there's still a "her" being attached to everything. The other girl knows she's taking it personal which is why she's saying she's not there yet.
Sansa kinda reminding me of Cersei more and more. Going through shyt like that would most likely change somebody for the worse. Maybe by the end of the season she gets the throne. Hope she doesn't go at Jon the way Cersei did Jaime though
. Starts thinking
"only half-sibling huh?"
I like the theory about maybe Meera being Jon Snow's sister or related in some fashion which lead to her to shattering a white walker rather than it being due to dragon glass.