What is Mrs. Snagsby's problem? What is comical about her behavior at the "improvement" of Jo?

She is very paranoid. She is sensitive enough to sense her husband's stress, but draws ridiculous conclusions about imagined clues. She does not trust him, nor anyone, and feels that things are going on behind her back. She is in a state of high alert, watching, examining, wondering and suspecting what her husband might be up to. When the ridiculous preacher Chaband begins his oratory, he singles out Mr. Snagsby, using him as a visual focus for his rhetorical questions, illustrations and sweeping moralizing. Mrs. Snagsby deduces from this that young Jo, the subject of this dissertation, who is now asleep, is the spawn of her husband. She breaks into hysterical crying and has to be removed from the room.