I mainly picked Lilo to dress up as Arya because she's one of the only Disney protagonists who's just a little girl (I mean in the books Arya's only like nine!!). It's been a while since I saw Lilo and Stitch, but if I recall, Lilo was kind of spunky, if not as morbid or bloodthirsty as everyone's favorite cross-dressing Stark.
Awe this is so cool and cute. I could see Lilo as Arya but like one of the comments bellow Vanellope might be a better fit personality wise- as Arya is a little rough around the edges like Vanellope while Lilo is more sweet. If you were to switch it then Lilo would be Shireen Baratheon as they are both sweet kind innocent quirky little girls. T_T