Game of Thrones did not include Lady Stoneheart because of her planned arc in the books and because her appearance could have cheapened other major events in the show's plot. The critically-acclaimed fantasy-drama was based on the A Song of Ice and Fire series of novels by George R.R. Martin. The books, however, are far from completion, and so showrunners David Benioff and D.B. Weiss had to juggle what was in the novels, what they knew Martin had planned, what they didn't know, and what they'd already shown when crafting the series. Lady Stoneheart did not make the cut.
Spoilers for the novels ahead: In the books, Lady Stoneheart is a resurrected Catelyn Stark, who becomes leader of the Brotherhood Without Banners and is consumed by a desire for vengeance against House Frey after her and her eldest son Robb's deaths at the Red Wedding. She seeks to punish those who wronged her and her family, a silent corpse just as cunning in death as she was in life. The character is a fan favorite due to the surprise of her initial reveal, but she has only appeared twice in the books so far.
Weiss and Benioff decided against including her because of her minimal appearances in the books and her effect on the rest of the show. Speaking to Entertainment Weekly, the duo clarified that their reasons for not including Lady Stonheart were threefold. Firstly, they had an inclination of what Martin planned to do with the character, and thought including her would have spoiled those upcoming events. Secondly, even back in season 3, they knew that in seasons 5 and 6 they would be killing off and resurrecting Jon Snow, which they wanted to be as impactful as possible. Lastly, the Red Wedding was one of the most iconic and lauded scenes in the entire series, and the finality of Catelyn Stark's death would have been cheapened if she came back. What's more, they felt that placing actress Michelle Fairley in a totally silent role would have been squandering her immense talent.
If fans are at all disappointed by their reasoning, they won't find themselves alone, as Martin himself expressed his wish to see Lady Stoneheart in the series. Her role will no doubt become even greater in the books, but Benioff and Weiss could not wait that long. The TV show was massively successful, so they must have done something right in their adaptation. The pair didn't always knock it out of the park, but perhaps Lady Stoneheart's exclusion was a wise move on their part. They didn't totally abandon the significant role she plays in the books, attributing aspects of the zombie-with-a-vengeance among the show's cast.
Those clamoring to see Lady Stoneheart in the rotting flesh need not give up hope just yet. HBO is keen to expand the Game of Thrones television universe with a prequel series already set for 2022. As more and more auxiliary installments take us back to Westeros, it's not too far fetched to think Lady Stoneheart may yet get her time in the limelight. Given the questionable ending of the series, HBO could look to adapt the eventual ending of the novels in which Lady Stoneheart will no doubt play a pivotal role.
Source: Entertainment Weekly