Her vertical recovery is good, but her horizontal recovery is godly (at least from what I've played on PM), she literally cannot die from being thrown far from the stage unless she reaches a blast edge, she basically flies all over the place with Ignis.
Any idea on why the Aether shield glitch happens?

I think I found a glitch with Aether in the PM version (dunno if it's the same in vBrawl though): if you do the move near the edge of the stage/platform and your opponent shields it you'll just keep going past him and won't stop until you reach the blast edge of the stage (so basically it's a free KO if he blocks it).

I think the same happened with Astra once but I can't replicate it.