I'm betting this is because rofiern uses the same summons. If so it would require creating a new series of identical summons for Az'atta just with different shields.
-TV
Edit: Acctually, I'm completely wrong. The guardians are rofieren summons, you seem to be getting the wrong summons. The hound archon is Az'atta's 5th level summon (according to the handbook) and the high guardian is rofiren's 4th level summon. Az'atta's 4th should be the lantern archon. You should get your diety field examined.