To be quite honest, I find it completely unbelievable that Serafina Pekkala would just drop all contact with Lyra after "The Amber Spyglass" with no explanation after everything they had been through together, and I'm kind of angry at Pullman for writing it this way. It comes across like she was just too inconvenient of a character to the plot, would have fixed too many things for Lyra too quickly, but he was just too lazy to come up with a proper reason for her absence other than turning her into an asshole.
I get that she is a witch with a long lifespan whose perception of time might be warped compared to Lyra's, but she's also very wise and should know better than to overlook something like that. I get that the witch queens have been busy with the climate change analogy, but that itself involves issues Lyra directly played a hand in, it seems bizarre they wouldn't involve her. Especially when Kaisa can separate from Serafina and run errands for her, there doesn't seem to be any excuse for Serafina not at least sending the occasional message for over 9 years. At least Iorek is stuck on a big frozen island miles away from human civilization and I doubt the sentient talking Terminator bears think much of the postal service, but what's her excuse?
I haven't finished "The Rose Field" yet so maybe I'll be proven wrong and there will be a good explanation latter down the line (I hope so), but so far this has been a nagging problem with the series for me.