Hmmm.... Jordan however contradicted all this. He said Siuan was too distracted and not paying attention. That's why the attack took her by surprise, that's why she didn't feel her warder being killed before the women entered the room.

What you suggest doesn't make much sense anyway. If Mesaana held Siuan with an inverted shield, the other captors would have felt that Siuan was already shielded by a shield they couldn't see or sense.... They would have known something really weird and terrinly wrong happened. Mesaana would never have risked anything like that, and beside, this likely was impossible, at the same time she was masking her real strength to pretend to have Danelle's.

Siuan was shielded before she saw the glow on Elaida simply enough because Elaida wasn't the one who threw the shield at her. The women still in the anteroom must have done it, while Elaida distracted Siuan by entering the room without having embraced saidar yet. When the shield fell in place, Elaida embraced saidar. That's all.