The Creator anon
Remembering the preview, it looked more like an ambush to start off the second encounter after her challenge. Now that Korra's actually starting to be able to air bend, it does seem likely that she would be able to go into the Avatar State in Episode 4.
Aang was able to go into the Avatar State soon after learning he was the Avatar. It appears, though, they can't just go into it whenever they want unless they master the spiritual aspect. Otherwise, it can kick in as a defense mechanism.