You can read Sansa two ways:
1- In her first chapter (and through Arya's) she is depicted as someone who doesn't like the north, wants to live in KL and be a princess like in the story books. She doesn't consider Jon her brother, she corrects Arya who calls him their brother by saying "HALF-brother". She is selfish, she doesn't care about being Stark. She says the north is basically a dumb and not worth seeing when Arya says the carriage won't have windows and Arya says it's awesome and she should know if she came with them sometimes out of Winterfell. It goes on like this. You can imagine she hasn't changed, she is just using her people for protection. That she still wants out, she still wants to be queen, and the people of the north are just her support, not her love, and the north itself she could care for little less other than as a place of support. In this case, what she did learn from Littlefinger is to use the north just like he planned to use it, and she is his continuity, acting in her own interest like he acted in his.
2- Or, you can see her as someone who wanted to leave and didn't care for the north or her family much and all the above, but now that she has seen what the "real world" is like she realizes the north is her home, what it means to be a Stark, etc. That she has changed. And what she learned from Littlefinger has not corrupted her, that it just made her smarter/wiser to make her way through the politics without being a pawn.