Make Annie's ultimate more meaningful to her kit
For a champion who's been around as long as Annie has, it's kind of surprising how pointless her ultimate is, if you think about it. The most terrifying thing about Annie casting Tibbers is that there's an instant AoE stun that does a lot of damage, and the stunning effect isn't even based on the ultimate, it's part of her passive. Strictly speaking, Annie's ultimate is basically a high damage AoE spell that creates a beefy controllable minion; that's a really boring ultimate!
Recently, Tibbers was buffed to receive an extra effect from one of Annie's spells, he moves fast and gains her shield whenever she casts it. I believe this is a step in the right direction. Why not go all out and make it so that every one of her spells affects Tibbers meaningfully? Thematically it is very clear that Annie's summon is suppose to be part of her identity (she talks about him constantly for one) but mechanically he's just a side effect. "Woo I stunned everyone and won the team fight! I guess I'll just... make Tibbers tank that tower and die now." While on the onset of Annies creation you may not have had the tools to add many meaningful interactions between her and her pet, I believe now she is due for a revamp that isn't really talked about as much as it should.