The chapter you want to focus on is Chapter Twelve in Book the Second, entitled "Down." This of course details the way in which Louisa has sunk to her lowest point and is completely unsure about which way to go. She feels some passion in her heart for the coldly manipulative Harthouse, but at the same time feels deeply confused. The method of education which has been strictly used to bring Louisa up, focusing on facts alone, has not served her at all well, and she herself says to her father that she "curses" the hour that resulted in her life being the way that it is. Note the emotive language she uses in describing to her father what he has done to her through his fact-based educational philosophy:
"How could you give me life, and take from me all the inappreciable things that raise it from the state of conscious death? Where are the graces of my soul? Where are the sentiments of my heart? What have you done, O father, what have you done, with the garden that should have bloomed once, in this great wilderness here!"
She struck herself with both her hands upon her bosom.
Thus we can see that Louisa experiences an emotional breakdown at this stage of the novel precisely because she realises how woefully unprepared she is to face life through the impact of her father's teaching upon her. She describes her life, that has had every emotion and natural fancy carefully and callously bred out of it, as a "state of conscious death." She has no "graces" of her soul, nor "sentiments" of her heart. Carefully tended, her soul and heart should have been a blooming and beautiful "garden," but thanks to her father, it is only a "great wilderness." It is this realisation, triggered by the advances of Harthouse and her own mixed feelings, that have initiated her own breakdown. She is a character to be pitied tremendously.