I checked the CR of the corrupted avatar and it checks in at 8 (6 for defense and 10 for offense), so I am guess that editorial error is with the text not the stat block. It was probably changed at some point.I think that may be right. It’s an 8th level adventure and without the legendary action it seems underpowered.
It is a corrupted avatar, not her true avatar. It is corrupted by another gods influence if I read it correctly.Darnit Wizards! Why you gotta mess with my favorite goddess, and make her avatar evil???? That's an abomination, man!
Avatar's allow a deity to be in many places at once. They have many uses and are helpful in spready a deities influence.Also, since Lurue is native to Faerun, why does she need an avatar at all?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.