Anivia win rate is lower the longer the game goes on
Champion.gg - Anivia Middle Stats, Builds, Runes, Masteries and Counters
I mean she's designed to keep the game going until her team can win though her win late the longer the game goes on is super low. I think riot has changed her focus in the game to weird point to where she's gotta snowball early and end the game early.