So many parallels to journey of flower! But I think the directors deliberately made the lead Bai Quan much more human and less of a happy go lucky (but lovable) airhead on purpose. She has claws in this one. That said...
This contains spoilers.
Our Bai Quan or Su Yin is heartbroken when the beautiful Li Jing a.k.a second ghost Prince has an affair with her (cousin?) Xuan Nu. She actually walks in on them. He says thy wouldn't work out because of her inability to abandon all and go with him. He leaves with Xuan Nu and returns home even though it's been clear from early on that he is confused about his feelings for Xuan. Well his father is not happy to see him and believing he will be killed Xuan Nu sells out her people to spy. She is deeply in love.
This selling out appears to cause Like Jing to realize he never loved her. He leaves without consummating their marriage and shortly after the power hungry first Prince shows up and drags her off to an unpleasant fate. We later learn she has been brutally beaten and returned to Kunlan as a warning. Bai Quan warns her to stay away or she might cut her. An extremely bitter and vengeful Xuan Yu is shown planning to use the trick of appearing like Bai Quan to steal a military strategy from the war God.
That said, I am very sympathetic to Xuan Yu. She tricked Li Jing once but he chose to keep sleeping with her after he found out dismissing the first time as h being g confused by alochol because she looks similar to Bai Quan. At one point Xuan Yu even tells him to pretend it didn't happen but she loves him and is able to seduce him without any more tricks. All is fair in love and war.
Now she literally throws everything away including her honor and family to keep him alive. He abandons her by telling her he loves Bai Quan and then she is tortured (this may be part of ghost Kings plot) and her lover has abandoned her. Naturally she will hate Bai Quan and want some payback. It's very tragic. And I don't excuse her behavior at all but her hate has a source and isn't random or odd. She played a big hand and lost.
Random funny thing: Dijun who I love bc he is so I dunno detached and has white hair is chatting about tea cups on the eve of celestial world war.