Everything you need to understand or teach Aunt Florrie by Robert Westall.
A middle-class English family has long had a Christmas problem: Aunt Florrie. For forty years she has arrived early on Christmas day, tormenting the family with nonstop talk and eating up their dinner and seasonal treats. Three generations of the family have submitted to her Christmas tyranny and endured the misery she brings. Then, inevitably, she dies.
Normal, enjoyable, quiet Christmases seem to be in the family's future. Yet, two years later a note from Aunt Florrie arrives, mentioning that she will, as usual, be over for Christmas. It has a recent postmark; the family's father takes the note to the police, who owe him favors, and they determine that "It's no forgery." Will, as younger brother Stan suggests, Aunt Florrie return as a vampire or another one of the undead?