I think that we have yet to see the full character transformation of Sansa. I am just now finally about to finish the first book so her being a selfish child who only cared about herself is still very fresh.

She went to Cersei and told her of Neds plans to send Arya and Sansa north, and that was when Cersei had Ned's guards killed. If we see her submit to Jon and not try to usurp his position in the north I think it will sort of complete her transformation. When Ned is taken prisoner she doesn't even ask about Aryas safety, she only begs the queen to let her marry Joff still, thinking she'll be able to convince him to exile Ned. If she does try to take power from Jon, I think it will cement her as only ever being interested in her own status.

She may not commit horrible acts as other characters but she played a big role in her fathers demise through selfishly wanting to become queen. She was just a child when that happened though so I don't think she can be judged too harshly as she didn't fully know the ramifications.

Either way, the last time Arya saw Sansa, that was who she was. She lied to the court about the events that lead to the death of the butchers boy and I don't think Arya has had time to forgive her for it.