About the magic sandstorm
"I think we're supposed to infer from Hermes' concern that the sandstorm is connected to the Girdle, and now that the Girdle is "active" once again and rejecting its guardians, it's revoking that protection. This would absolve Diana of any wrongdoing in taking the Girdle, and make sense in the context of Perez' general writing style, but I'm still not totally clear on how the sandstorm is supposed to have started up in the first place. Maybe an early Bana sorcerer created the storm and drew on the power of the Girdle to sustain it".
You missed the comment made in the beginning of WW 35 that the Sandstorm was created by the blessing of a "long forgotten goddess" , hinting that the Banas once had other cults besides the martyr worship of Phthia.