How to Nerf Annie: Remove her stun or make it have a timer.
Removing the stun would leave her as complete trash. It's a terrible idea. If you really think Annie is strong enough to lose that, then you need to reevaluate your opinion of her balance state. She's not so powerful that she can lose a core mechanic.
Giving it a timer is also a terrible idea. It focuses way, way too much on the laning phase. The thing about Annie is that in the midgame and lategame, almost all of her values comes from initiation. She doesn't really do anything else. If she loses the stun, she can't initiate, so she can't do anything. Giving it a timer either prevents her from being able to use the stun for initiation, or it forces her to spam abilities (W and E) on nothing for the purpose of stacking it up. The former kills her, and the latter is just stupid and insipid design. Spamming shit on nothing for most of the game is one of those big game design "DO NOT DO THIS" rules.
The fact of the matter is that Annie is balanced. If you want to remove something as core to her as her initiation potential, you need to find something to replace it.
