Her passive is both strong and weak. If you rate yourself 0-100 against her then you're doing it wrong.
She was once a powerful, even unassailable mid. She had free farm, heavy waveclear, super E and a bear that ate towers.
Annie has had a lot of changes. The last I clearly remember was another nerf to her E again, also stun durations start lower.
The one buff I know was a play flow change to reduce her cooldown on build-a-bear at levels two and three in R.
Now there are several super hard counters to her; in compensation she can 100-0 certain ragequit champs like Yasuo. :3
I have played her in all lanes and even jungle, the last is only possible if you have 30 and the enemy jg is not hard counter.
Annie can go tank but her AP ratios will reward traditional mage role more. Only go tank if your comp is boned and the team needs SOMEONE to tank.
RoA is a double edged sword on Annie. It badly slows down her early oppressive damage. But it gives the health and mana for long trades.
I like to rush DFG if I think I can snowball, with a Deathcap after that and probably spellvamp because super low health.
Some people build a Tear on her even though mana should not be a big deal, because high Q rate and endgame Seraph payoff to her AP ratios.
She is in a good place, well understood. Counters some champs and is countered by others. And trades with the rest.
I would like an AD ratio of some sort on Tibbers' physical auto attacks. AD/tank Annie with Tibb summon already melts towers, why not even faster?