To convey the truth about a character often takes stepping into the protagonist's shoes, be they flip flops, stilettos or boots to get to know her inside and out well enough to convey her truth. Often that takes exploring the dark side of ourselves.
By the 3rd draft, a writer slips on her own shoes and plots a point to the violence by revealing the truth about the character's coping strategies in scene through cause and effect. A powerful secondary character feels sympathy for the protagonist. He helps the reader, too, to feel sympathy rather than repulsion for her. The character may talk about killing everyone flippantly as a coping mechanism. Who she is is uniquely her. Her feeling are universal. Arrange the scenes to show the true cost to the character herself as she moves from denial to acceptance.
She enters the end, fully conscious of who she is and with a plan to get her where she thinks she has to go.
To familiarize yourself with the Universal Story and the basic plot terms in the above blog post:
1) Read The Plot Whisperer: Secrets of Story Structure Any Writer Can Master (Now also as a Kindle edition)
2) Watch the Plot Series: How Do I Plot a Novel, Memoir, Screenplay? on YouTube. A directory of all the steps to the series is to the right of this post. 27-step tutorial on Youtube
3 Watch the Monday Morning Plot Book Group Series on YouTube. A directory the book examples and plot elements discussed is to the left of this post.