User blog comment:FairyRaven/Fairy Tail Chapter 396: Air, Review and Commentary/@comment-24784846-20140812160110/@comment-24066070-20140812200738

As I said, she wasn't submerged as long as the others. So she still had some oxygen left to pass on to Gajeel.

If you see a massive torrent of water coming your way, a logical reaction is to inhale as much air as you can. Therefore, Levy had enough oxygen to save Gajeel. There is really nothing strange or exagerated about her being able to pass air to Gajeel.