During the first interview between Kate and Marlow, Kate was able to pinpoint on the fact that Marlow has an issue. The issue is that Marlow feels very uncomfortable when he speaks to women of his same social status (upper-class women). Yet, he is completely comfortable talking and mingling with lower class women.
Upon meeting his potential fiancee Kate Hardcastle, Marlow's issues immediately surface; yet, rather than taking his stuttering, lack of focus, and inability to look at her in the face as an insult, Kate plays with Marlow's weakness and finds it entertaining.
Part of her playfulness is evident when she makes a comment on the social hypocrisy that she believes is rampant in their day and age.
In this hypocritical age there are few that do not condemn in public what they practise in private, and think they pay every debt to virtue when they praise it.
Kate perceives Marlow's lack of comfort and she says this in order to elicit his point of view. Marlow continues to stutter and keeps being unable to make any sense of his answers. He agrees in that in their society people only act with virtue when they talk about it, but in their private lives they do as they wish. Yet, he also adds on a separate note, and with extreme difficulty, that sometimes the want of courage to do something makes people act differently than what they really are. Kate agrees by saying
I agree with you entirely; a want of courage upon
some occasions assumes the appearance of ignorance, and betrays us when we most want to excel. I beg you'll proceed.
Yet, Marlow cannot really proceed and shifts the conversation by suggesting that they go for Miss Neville in the adjacent room.
This being explained, there is no indication that Kate Hardcastle thinks that Marlow is a "hypocrite". She brings up the topic of hypocrisy as a way to taunt Marlow into seeing himself as a hypocrite because, after all, he can only be who he really is under specific circumstances; other than those circumstances, Marlow is his real self.
Kate knows this. Yet, notice how she softens the topic of hypocrisy and changes it to the possibility of "lacking courage". This means that, although Marlow's double personality is hypocritical in nature, Kate still understands the reasons behind it: it is not that Marlow intentionally changes personalities to hurt or praise people; he simply lacks to courage to accept who he is and who others are instead of judging people at face value.