Well, this is completely wishful thinking, but I hope she is returning this season. I could see why the show has held off on re-introducing her until now, considering that they have not revisited the Riverlands or the Freys basically since Cat's death. It seems to me that it would make sense for the show to only introduce her when they are full-scale committed to the Riverlands. Based on some of the casting rumors and other stuff, I'm optimistic the show is returning to the Riverlands and committed to telling that part of the story (which they should be, it's a huge part of the books). I've always maintained/hoped that Lady Stoneheart was too big a deal, both from a shock perspective, and more importantly from a narrative standpoint, to cut out completely, considering she is the link between Jaime and Brienne.
I've been what might be called a defender of this show for a while, but I found Season 5 to be extremely disappointing and not good at all really (outside of Hardhome imo)
Tough to defend Dorne, Winterfell, Stannis, and a lot of the changes. Dorne was an absolute mess and even worse, a complete waste of time on a show that claims it doesn't have enough of it. Winterfell was a disaster and doesn't hold up to any kind of rational scrutiny from a logical, storytelling perspective. Stannis I think could have been good, but it was extremely rushed and the show didn't do a good enough job of establishing his desperation in the key moment for him.
On the plus side, as mentioned above, Hardhome was brilliant, and I think a good editing/condensing job was done on Tyrion and Dany's arc in particular.
But yeah...all in all, when I look at what could have been, and what eventually was, I can't help but be extremely disappointed, mainly on the sheer stupidity and awfulness of Dorne and Winterfell. When I think of those 2 plots being adapted, I think of the knife's edge tension in Winterfell, Manderley and the North Remembers and Frey Pie, Dustin, the NORTH!!! and for Dorne, basically the Queenmaker plot and Fire and Blood. To cut those out for what we got...not to mention the UGH!!! involved in finding Jeyne Poole's storyline more important and engaging to tell than Sansa's...
To me, the biggest mistake the show made this season, and probably its history, was omitting the Manderleys. I mean, I don't see how that got cut. In a season full of gloom and doom, Manderley's "the North remembers" speech is one of the few triumphant positive moments. It would have been very memorable. Not to mention freaking Frey Pie, another one of those triumphant moments.
I really don't get how this show had time for Dorne, Grey Worm/Missandei, Meryn Trant's "too young", and several other nonsensical go-nowhere sideplots while it couldn't find time for Manderley.
I think it could have been a brilliant move to transpose "Alayne's" story in the Eyrie to Sansa in Winterfell, having Sansa "play the game" with Northern lords such as Manderley and Dustin. You could also use that to cut out the rape, as the show hinted that Roose was pressuring Ramsay to rein in his behavior, and certainly having Sansa and the whole "Northern conspiracy" watching Sansa's treatment carefully would provide justification for that.
But yeah...D & D needed a shocking moment so they just decided that Jeyne Poole's story was more important to tell than Sansa/Alayne's. Just really an awful disgusting decision on their parts imo.