Our first example of XLN being a psychopath comes when she's injured because of the interrupted practice of the Jade Maiden. And she's all - "Hey, I'm dying, Yang Guo. But I promised to take care of you for life. I have a brilliant plan, I'll kill you first. That way, I'll keep my promise."
...huh? Wow. Just a slight slippery grip on sanity there, girl.
And then there's all the things she's willing to do to cure Yang Guo of the poison of the Passion Flower. Which is pretty much kill anyone.
"I don't care if he raised you and you love him, why can't you let Guo Jing die so you can live?"
"Oh, Huang Rong is offering for me to kill her to get Yang Guo's cure. That's great."
"Oh, let's take Guo Xiang to Passionless Valley to get the cure. Even though she's a helpless newborn baby."
WTF? Heartless *****. Please, just die already. But, no, she's the heroine. She's the good guy. She's amazing. BS.