Lord Petyr Baelish organized for Sansa to be married to Ser Harry Hardyng, also known as "Harry the Heir," in "A Feast for Crows." His nickname reflects the fact that Harry Hardyng is heir to the Eyrie behind Robin/Robert Arryn (we'll call him Robin, his show name, to make things easier). Littlefinger indicated to Sansa in "A Feast for Crows" that sickly little boys like Robin Arryn die accidentally all the time, and if that were to happen, she and Harry Hardyng would take the Eyrie.

Harry isn't thrilled to be marrying her in "The Winds of Winter." This whole time she's been posing as Littlefinger's bastard daughter (not his niece as she's described in the show). He thinks he's above marrying a bastard and is annoyed he's pushed into it, but he'll probably perk up when he finds out that she's Sansa Stark.

The future is looking bright for Sansa, but not little Robin Arryn...