On Bella and Sinistra - all I can think of is that it has something to do with the centaurs and their prophecies in the stars (Harry reported that they were saying some esoteric, typical centaur things to him during one of his ventures into the Forbidden Forest). Is she supposed to study What the Stars Say About the LP (And How to Surpress Any Trouble They Predict)? It's all I can think of, at least, but I've never been good at guessing plot twists.