Sivir. Bird has such a huge hit box that it's extremely easy to hit Anivia both times on Boomerang. And since Flash Frost is so easily telegraphed, it's extremely easy to just negate it with Spell Shield and deny her the chill effect.
If you lane against her as Sivir, you are able to put her on the defensive and never allow her to get going. If she has a poor early/mid game, it's extremely difficult for Anivia to catch back up. As with all casters, as the game gets later and later, she becomes less viable.