Sansa being able to only "skinchange" with the animal that has the closet connection to humanity, the animal that is usually beaten and broken to follow the strictest law, the animal that was altered so much from its origin. It's poetic and sad, the symbolism of grrm by choosing the old hound being her only connection (which is forever broken an altered) to the wildness of her stark lineage that she has turned away from is fascinating.

While Arya embraces her wildness, she connects deeply with her stark heritage, her wolf although taken away (like Sansa's) has a chance in returning. Her deep connection not only with Nymeria but the wolves in her pack. Arya having a skinchanging abilities with the aloof and independent animal of the cat and the fierce family oriented animal of the wolf really drives home Arya's nature within herself.

exactly! dogs are not wild animals therefore they have a very close association with society. as does sansa bc of her conformity. dogs are similar and the easiest species to bond with so its no surprise sansa was able to foster a little connection to the old hound but even that goes nowhere. 

so yeah that loss has, irreversibly, weakened her connection to the wilderness plus a lot of other things by extension. the old gods, the north, her family. her siblings are starting to truly sense each other through their shared warg bond. i think this is going to become a very relevant plot point going forward. bran’s presence in arya’s twow wolf dreams was not subtle. with every book they get more powerful and closer to communicating with each other. but sansa is left out of that dynamic entirely. complete radio silence on the warg net and theres no sense of old gods in her story either. 

all of which is contrasted dramatically by arya who, unflinchingly and immediately, embraced her wolf in a way even most of her brothers cant compete with. arya is as far as she is with her skinchanging abilities bc she is NOT afraid of of the dark, wild parts of herself. arya is constantly relating to nature to help her navigate the world around her. even in castles or cities or across oceans her nature powers only keep growing. its not diminished at all.

shapeshifting into animals is something most would find uncomfortable (at best) and terrifying (at worst) theres a reason wargs have a fearsome reputation within the books. but arya is comfortable with that. arya already feels "bad" for her nonconformity and on account of the things she has done. unsurprisingly, sansa views arya the same way. how will she feel when she finds out her "wicked" little sister is a monster? now theres some rich soil for conflict.

lady died as little more than a pup so sansa never had to confront the truly monstrous nature of a direwolf. she cant even fathom it. she has built her identity on being a lady. that role is at odds with the wolf (hell, its at odds with her humanity too). will she reclaim a part of it someday? maybe. there is a small piece of lady that still lives within her. when sansa contemplates shoving joffrey to his death we see that part of her but its quickly suppressed. she lowers her eyes, submitting, and becomes the “good girl” again. that piece of sansa has yet to show itself again. it was a fleeting thing. but the story is going to get dark. idk that sansa can ignore it forever. at some point she is going to have to confront not just the darkness around her but within as well. 

regardless, she will never be as connected to wolves as her siblings. she will never become a wolf. that path is lost to her. forever. its symbolic and its tragic and its going to effect the plot and i love it. the warg bond in this series is one of my favorite elements even when its missing.