A maester could write tomes about all of the changes
Lady Stoneheart is the resurrected Catelyn Stark. Ser Beric Dondarrion brought her back to life with a kiss, which killed him. (Unlike the show, where he made to the Battle with the White Walkers, book Beric bows out of the story much earlier.) The mostly mute Lady Stoneheart, whose skin is gray and who still bears the throat wound from her execution, made her shocking return at the end of
She also made one appearance at the end of
Her appearance is one of the best, most shocking moments in the books. And she seems primed to play a major role in the story going forward. Which is why readers always anticipated Michelle Fairley’s return. She never did, and the series’ showrunners, who also said there was very little debate about using the character, told Hibberd there were three reasons why.
The first reason they wouldn’t get into the specifics of, because it would be a spoiler for Martin’s last two books. The last time Lady Stoneheart was seen she was demanding Brienne kill Jaime Lannister. Those two might have very, very different fates in the books than they did on the show.
The second reason had to do with Jon Snow. Benioff and Weiss long knew they’d be bringing the Lord Commander back from the dead and they didn’t want to lessen the impact or shock of that moment by bringing back another major character too.
Finally, they thought bringing back Fairley for a primarily non-speaking role would not be fair to her or her great final scene. They didn’t want to retroactively lessen the impact of the iconic Red Wedding’s last moment, one of the best in the show’s run.
Martin disagreed with their decision to exclude her, and a lot of book readers still do. The Red Wedding is even more devastating in the books, and Lady Stoneheart’s shocking return doesn’t change that. Also, the character is fascinating and offers so much promise for amazing future plot twists. And Michelle Fairley, whose onscreen rage was incredible, could have excelled in the role.
So while Benioff and Weiss had their logical, defensible reasons for not including her, that doesn’t mean they were right.