Why did she do what she did ?
That’s a very good question! I’m afraid I don’t have a satisfying answer for you, since she doesn’t really have a logical motive. I portrayed the character as a psychopath, and if you read through the story, you’ll hopefully find hints here and there pointing towards that behavior.
If anything, her reason for doing what she did is just for the sake of fun. As many serial killers expressed, they basically murder to get their rocks off. It makes them feel emotions and sensations they otherwise would not be able to due to their condition.