She is in an decent spot with balance right now in the mid lane, where she can do well into some champions and be completely destroyed against other match ups. Top lane is her "off-meta" or barely played lane where she is almost never seen there ever, so you want to nerf her and make her trash mid lane as well?
And you can do something...if you are a tank, build some MR and laugh at her damage since the bulk of her damage is in her E or prolonged ultimate, which destroys her mana bar even with 2 mana items. If you are a fighter, save your dash or what ever you have for when she tries to Ult + Wall you, or if you have any hard CC then use it on her the second she drops her ultimate so you can instantly cancel it. Pre level 6 Anivia is 100% about her Q which is very slow and easy to dodge, in most cases the Anivia player is usually forced to either use her wall to slow or pin you down for her Q or get close enough so you won't have time to dodge it. If she misses her Q then she has literally no damage until it's back up since her base E damage is a joke.
Also Teemo does more damage since he does a lot of damage over time where you can't really stop him besides killing him or running. Anivia's damage is all about her empowered E or keeping people in her ultimate for most of her damage. Teemo has no "counterplay" about any of his abilities, as he is all point and click, auto attacks or his shrooms which only real counter is sweeper.
If you get into a fight with Teemo, he'll just Q you and auto attack you to death and run you down, while his auto attacks deal a lot of damage and his Q is a pretty low cool down, and if you try to jump on him...he'll run away into his shrooms and kite you to death. Anivia's burst comes from her E which while it is a target spell, it relies on the use of a slow moving Q or a prolonged ultimate that you can CC her to stop, or just walk out and if you survive her initial burst, she really has nothing else until either her Q comes back up or her ult + wall comes back up.
You just need to know how to fight her, and honestly...how often do you see Anivia top? Because I hardly ever see Anivia even being played mid, not even going to think of how rare I see Anivia played top.