Why is Mrs. Reeds is so cruel to Jane?

Mrs. Reed promised her late husband, Mr. Reed, that she would support Jane after his death. While Mrs. Reed spoils her children John, Georgiana, and Eliza, she does not feel any connection to Jane. Mrs. Reed views Jane as a burden that she was forced into supporting.
Moreover, Jane does not act submissively toward Mrs. Reed as Mrs. Reed believes a typical girl should. Instead, Jane voices protest over her aunt's cruelty and undermines her authority. For instance, Mrs. Reed instructs Miss Abbott and Bessie to bring Jane to the Red Room as punishment for hitting John. Jane physically resists the servants's efforts before she is forcefully locked into the room.
In Chapter 21, Mrs. Reed addresses Jane while on her deathbed:

Because I disliked you too fixedly and thoroughly ever to lend a hand in lifting you to prosperity. I could not forget your conduct to me, Jane—the fury with which you once turned on me; the tone in which you declared you abhorred me the worst of anybody in the world; the unchildlike look and voice with which you affirmed that the very thought of me made you sick, and asserted that I had treated you with miserable cruelty. I could not forget my own sensations when you thus started up and poured out the venom of your mind: I felt fear as if an animal that I had struck or pushed had looked up at me with human eyes and cursed me in a man's voice.

Mrs. Reed became determined to dislike Jane from the beginning. Through all of Jane's protests and displays of emotion, Mrs. Reed came to recognize her niece's humanity. As a result, she felt guilt to the point of fear for treating Jane like an animal.