Well, for Satori, she has very little idea of Alaria's own weakness regarding Psychomancy. I don't imagine that Alaria freely tells everyone of what happens, and Satori only knows it exist, but not to what extent. Her purpose in poking into Alaria's mind was to witness firsthand what actually happens, because she doesn't know. This is of course not the place for such a sensitive experiment, but unlike the others Satori didn't even enter Alaria's mind, she just poked it. And even than she has no idea what would happen to Alaria or how she'd react, because Alaria is the first one of this instance to ever show up at the college.

You'd have to understand, even though Alaria's weakness to Psychomancy is just that, Satori (And bit by extension, me) needed to know just [i]how[/i] sensitive Alaria is to Psychomancy. ALL Psychomancy involves probing and altering the mind; even visual illusions like flashes of light involves entering the mind of someone and making them perceive those lights. If Alaria can react violently to something as minor as Satori just poking into her mind, who knows what would happen to more elaborate and powerful spells; including ones that are suppose to be very subtle. Alaria's sensitivity to Psychomancy can be used as both a weakness and a strength; if she can pick up to something as subtle and pointless as a poke in her mind, what stops her from reacting to much more powerful wide-area illusions that is suppose to go unnoticed? Even though Alaria can't resist all illusions, her weakness allows her to know when she is being affected by illusions, when others can't. And that is a very important factor when fighting against illusionists.