Sirius has hidden a little more than he let on-
being left at the altar, excuciating jealousy of Barty Crouch Jr., but a daughter? This is new, even for him.
Even Snape knows her better than Sirius does and George keeps shooting her glances when no one's looking. After a trip to Antonin Dolohov's house for a little hunting, Harry feels he may be getting a bit more out of Christmas than he bargained for.