"I don't think I can," Suiko says, "accidentally" falling with the teacher's assistant. "You're slipping right through my grip. It's like...like trying to hold on to sand. How did he manage this?" Her tone is more curious than horrified, which, really, is her more likely reaction to actually having a fellow student be transformed into inanimate sand.

In case that isn't enough, she decides to spin another illusion over Patricia's mind, clouding her senses enough that she might genuinely believe she's being transformed.

Spoiler: OOC
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Going for a silent image this time, replacing visible skin with sand. Will DC 17 to resist, concealed spell with a +1 bonus on the check.
Concentration: (1d20+9)[18]