Please change 
's Flash Frost from "if Anivia activates the spell again" to "if an enemy champion is hit"
You shouldn't need to recast it. It should just stun if it hits a champion. It is already the slowest moving skill shot in the game. It is way too easy to prevent the stun by counter CCing Anivia.
So tanks can simply block it ? no ty. You have the W and R to set up the Q so it's not like you need to land it max range on a 500ms target ever.
Now, adding a small case of "if anivia is unable to recast her Q(because of non-self induced CC) at the timing it hits an enemy champion, Flash Frost will auto detonate" would be the best of both worlds, but do you really trust riot to implement this? xD
