It seems like the realities of the TV show.....limited time to tell the entire book series (funny, but you would think that 70 hours of time would allow for close to everything, but it doesn't turn out that way).
I assume a lot of these eliminations (smaller characters/storylines) have to go. But interesting that it seems like the Mountain is returning.
What to make of this? 
First, the actress may be lying. She would hardly be the first to do that. It could well have to be filed under the same heading as "JJ Abrams isn't directing SW" and similar "white lies". The thing is, cutting LS would force them to radically alter Brienne's storyline, and this in turn changes completely the dynamic with Jaime. LS, in the books is also the example of a Red God's wight, so she might be more relevant to the war of Ice and Fire than we know.
It's hard to predict how they might do this as we'll know mostly after WOW is out and we see where the Jaime/Brienne arc is going. Maybe there's a way to.get this back on track for them without LS or the BC, but it's hard to see. It's also hard to see what alternative arc they may give Brienne and Pod, or what they would gain by that.
What's strange is that they built up to LS, that is with Brienne's arc and her Oath, but also by including the resurrection of Beric etc. I'm less surprised that they don't wish to return to the Riverlands for a continuation of that war, or to send Jaime there (there's a rumor he might go to Dorne instead) but LS is just a couple of scenes... It's a weird decision, if it turns out to be true, but it would be safer to wait for the show runners or GRMM to confirm what the actress said. If they don't, it will be fishy. And technically LS was Catelyn, but Catelyn is dead and LS is a very different woman, so...
That said, LS is a bit lame, so it's not something to cry much over if they cut her.
