[X] Use grief to generate quiet sound in Mami's ear.
-[X] "Timestop, now!"
[X] Rionna's soul gem is a ring on her finger right now. Cut her hand off with grief, do not touch gem with grief, use hand for moving about if absolutely necessary. Keep soul gem in privacy sphere, to isolate from enslaved souls. Avoid contact so she can't act in timestop.
[X] Use grief to encapsulate Rionna without touching her, and flash-vaporize Rionna's body.
[X] Stay calm. Keep talking. Obviously, what Riona's done is massively fucked up. But you can't start a fight here, not with all these people around. Get more information, and get Rionna away from the muggles. Perhaps you could show her Warehouse-kun?