Professor Trelawney predicted the many deaths in the Battle of Hogwarts years before Harry even had his first Divination class (including Harry's own death) Basically the title As Professor McGonagall said, every year Professor Trelawney predicts the death of at least one student. Divination doesn't specifically predict When things will happen, just That they will happen. So what if each student she predicted the death of died later at the Battle of Hogwarts or during Voldemort's Reign of Terror? She also predicted Harry would die, which he did, just not that year, along with her many other predictions that came true, like Lavender's pet rabbit dying. Trelawney was a very capable Seer, just misunderstood and doubted by almost everyone. Just something that popped into my head whilst reading Prisoner Of Azkaban again.