Great session - great pic. When I see those pictures I always wonder how this must feel: Sinking into that warm and sticky mud, beeing covered completely from head to toe.
Maybe I'd panic when eyes and ears are clogged and I lose orientation but it's definitely worth a try.
Next time, how about leaving her a breathing hold, using fast setting plaster and then applying the vibrator only when the plaster has hardened. That way her climax can crack the mold!