Sokka and Katara run into them while trying to get to bumis castle (Omashu episode has Jet, Omashu, Northern Air Temple, Cave of Two Lovers and the Iroh captured by earthbenders all in one)
ok their reasoning is, Aang "can only call upon the past avatars when hes in their shrines" which makes absolutely no sense as she moved OUTSIDE of her shrine
Kyoshi telling Aang about the avatar state and then posessing him to defend Kyoshi (from Zhao AND Zuko on different fronts) is interesting and just totally steals that beat from Roku which is makes more sense for.