User blog comment:Western Gen/Speculations for Season 12/@comment-10990964-20131112182213/@comment-4616231-20131114004118

Well, you just answered your own question there, pretty much. Obviously, if they CAN use her in Halo 4, then she must be in Halo 3 for a different reason. Probably story-related.

Also Eta and Iota did literally nothing.