That's the thing - Theon killed the ones who were there and Bran/Rickon/Hodor/Osha fled. The rest were killed/imprisoned with Ned in King's Landing. (In the book, a couple of other important folks get away.) So the people in Winterfell at that time would not recognize her. The only person who knows for sure is Reek, though it is mentioned a couple of times that the Boltons were made aware and just don't care since nobody else will notice. The key is that there's a difference between the people who were loyal to the Starks but didn't live at Winterfell and the actual Winterfell garrison, so for the people attending the wedding, Jeyne matches the description of a slightly older Arya Stark.
The other thing that was removed was that Petyr made Sansa alter her appearance and become Alayne Stone, his bastard daughter. Nobody knows she's Sansa in the books except him.
The reason I spoiler tagged the one portion is in case it ends up happening in the show, btw. I hope it does. The fifth book did have some good story lines in the Theon/Davos chapters so I'm still keeping my fingers crossed that some of it survived the cutting/conflating/replacement.
Bookmarks