Mrs. Sparsit continues to show excessive pity to Mr. Bounderby when he is present, and excessive contempt to his portrait when he is gone. Watching the progression of Louisa and James Harthouse's relationship, Mrs. Sparsit rather evilly gets it into her mind that Louisa is slowly descending a great spiral staircase, and when she gets to the bottom – which, Mrs. Sparsit imagines, will be when she ruins herself and her honor through her affair with Mr. Harthouse – then, how Mrs. Sparsit will rejoice!
While the satisfaction Mrs. Sparsit takes in watching Louisa's downfall is malevolent, it's clear that this is not going to end well for Louisa, who is allowing herself to be spun ever more securely into Mr. Harthouse's pleasant web of flattery and careless affection. As Mrs. Sparsit sees, this will end in utter disgrace for Louisa if things continue the way they are going.
In one of their conversations, which Mrs. Sparsit spies on through a window but can't overhear, Mr. Harthouse manages to persuade Louisa that Stephen, whom she thought to be a just man, may very well have succumbed to the temptation of stealing the money, because that's just the way the hands are. Louisa allows herself to be persuaded by him, which makes her feel both bad and relieved.
Louisa here betrays a very feminine trait: that of closing her eyes to the likely truth of the matter and going along in the deception when someone she loves, Tom, might actually be guilty. Note how casually Harthouse assumes that Stephen must be no good because he is poor. The wealthy create a system that impoverishes the working class, then sees that working class as being worthless and shifty because they are poor.