Katrin keeps her hand on her sword until Lissa's explanation is over, unsure whether or not Khazrael or Lissa is 'posessed', as Aldamar put it. The gnome's frantic explanation matched up with what Yix had projected in their minds, and her actions certainly seemed to be in-character.

Katrin is saddened when she notices the lizardman's disappearance. If he has gone to fight the aboleth, at least he will have died fighting; it's probably the way he would have wanted to go. He will be sorely missed.