You learn a bit about her backstory without her spilling her guts through that echo flashback. You see that her "parents" hated her and ignored her, you saw that she was tossed aside and treated like an outsider. She barely felt Doman, as she wasn't even good enough to serve the imperials as one. She also lost her mother at a young age, as she was under her aunts care who wanted nothing to do with her. We don't know how she lost her mother, but it may have played a part in her tragedy.
When she spills her guts about being beaten, abused, and sold - all by her very own Doman people, she began to despise them, feel like she wasn't one of them, not worthy of their gaze. Her upbringing was broken, she had nothing and therefore could feel nothing but negativity. She was full of hate, and the only way she felt anything was seeing people suffer, especially those who she believes wronged her because of their blood. Her spilling her guts at the last moment is her playing her part as the tragic villain, and she knows how cliche it is, but also buying herself some time to get one last one-up over you. She is evil, tragically evil. Even her shooting Gosetsu as he tried to save anyone was just enough to cement her in as this broken, lost cause of a woman. She had nothing, knew nothing other than pain and making people suffer. At the end, she starts to cry and you see that there was some human beneath all that hatred. Still, it wasn't enough and it was far too late, and she died being crushed under a castle she brought down on herself.
Reasons why she's one of my favorite characters - I have a real soft spot for tragic villains, especially ones who go off the deep end and have some clear psychological issue due to events that seem rather realistic. With her having all the ingredients to be a horrific villain, it's typically a recipe for faceplams, groans, and disaster. However, I think she was very well acted thanks to her voice actress, and well written. She was deliciously evil, her voice cracked and changed as emotion ran through her, as if she wasn't exactly sure how to feel or act when she wasn't hurting people. She makes you hate her, want to punch her face in and kill her in the most brutal way possible just to get back at her. She didn't want to take over the world or destroy it. She wanted her tower, she wanted her power over people and control, she wanted to continue ruling and hurting people as a means to get off, to feel anything. In the end, she got exactly what she deserved. I enjoyed her ending and how she was forced to come to terms with her own death seconds before it happened, as if she'd never considered it while making people kill themselves or others. I'm just glad there was no forgiveness, no sudden "I'm good now!", no redemption for her. She was a villain with her own reasons, as misguided and insane as they seem. It was just evil through and through for reasons that I could understand. While I don't agree with them, I see where she came from and why she did it, even if it was too damn far.