Summon Aery just doesn't work with Sona's W.
this is super easy to test; all you need to do is go into any game, level W, and hit a champion with her W. Aery doesn't fly to them. there's no additional shielding. this is pretty potent bug, missing out on a good amount of shielding.
i'm also not sure if this is a "bug", but, Summon Aery seems to be able to apply on up to 3 enemy champions at a time, all on separate cool downs. i'm not sure about the allied champions, but, i believe it's only 2 (or 5 total).