Even Susan. I carefully ensured that someone noticed that there was a gap. oooo -- foreshadowing. how clever of me.
The problem is that Susan is a POV character.
I need to put something in the letter that will foreshadow the final conflict. Not too sharply. Being the final conflict, it needs to build thorugh the story. Even the trouble it causes her parents can't be too much, because if they vanish soon, the story will escalate too soon.
The timing is not, however, the big thing. The big thing is that I have to figure out what on earth is the core of the problem. It orphaned Tam in the backstory, it has had more subtle influences on all of them (except, perhaps, Loveday), and it's going to go after Susan's parents. That's not an actual problem. That's just its results.
Well, I think it involves another character. A woman and a wizard. So whatever it is, even if not human, it can deal with humans. (Superior or inferior? Don't think it would be an equal.)