She's just depressed that her little sister was the one to get the most brutal kill on the show.

Book 1: Looses bending in order to save the last airbenders. They get caught regardless.
Book 2: Stays in republic city dealing with incompetent detectives and an over his head beat cop. City gets wrecked by giant spirit monster.
Book 3: has to deal with bitch half sister who makes problems, starts shit, and never apologizes. Tries to keep the Avatar safe. Avatar gets captured, poisoned, and put in a wheelchair.
Book 4: tries to save family and protect the city from Kuvira. City gets blown the fuck up.