Reading an Alayne chapter now.
"This morning her eye was caught by a parti-colored gown of Tully red and blue". Sansa isn't a Stark. Which always is *fine*. It's not that Sansa is detestable, it's that she's not aspirational. In the books for sure she's not worthy of the Stark name, and she really isn't in the show either.
As far as "training" under Littlefinger... it's nice to think that because we want her to step up but here's the releveant scene: shortly after Lyssa's death, Robin takes to sneaking into Sansa's bed. Sansa doesn't like this, and has a guard lock her door (I guess it only locks from the outside?). One night (occasionally, in fact), she forgets to have the door locked and Robin comes in and nuzzles her breast all night. Robin is literally he easiest dude to rebuff but she never does, she just rolls with it.
Someone saying early she found a maternal instinct with Robin? Nah. She just lets Robin happen to her. She lets everything happen to her. She comes to accept things, fine, but she never pursues anything.
The show and book make major diversions with regard to her situation, but they basically preserve her disposition. Sansa is an object to other subjects' verbs. Littlefinger takes *her* under his wing, Robin makes *her* into a mother, Bolton marries *her*, Ramsay rapes *her*, etc etc etc.