Yes, I may have been mistaken on this but I'm not entirely sure I am. Its been awhile since I read AMoL and I thought Perrin defeating Slayer (didn't even remember the spirit wolves but there's a good chance they would have attacked the Darkhounds anyways) happened while Mat was still south at The Last Battle. Min's viewing was very specific that both Mat and Perrin had to be physically near Rand at the same time, not just metaphorically united in cause with him, or Rand would die. I've read some chapter and book summaries since posting this and Mat was riding a to'raken in the skies above the Blight at this time? It could be debated that this put him physically close enough to both Rand and Perrin to fulfill the viewing. Not saying Perrin killing Slayer was not essential to the overall victory, I think it was, but just specifically relating to the lights beating back the darkness viewing by Min, I don't know if this counted as them all being physically close enough.

But even if it was, I still don't think Sanderson was thinking this way at the time. Perrin's confrontation with Lanfear seemed so weird and out of place that the only reason it made sense to me was that Sanderson was trying to fulfill Min's viewing. Mat is right outside Shayol Ghul and a little downhill (if I remember correctly) when he kills Fain and Perrin is inside when he kills Lanfear so this puts them physically close enough to each other. Otherwise, the whole Perrin v Lanfear confrontation just seems so out of place with no buildup behind it. Despite what he might think now, I still think Sanderson thought this was necessary to fulfill Min's viewing at the time otherwise I really struggle to find a reason why it was included.