I think people often misunderstand why she became a villain so I’m going to lay it out here. (this is, ofc my understanding of it and others may have other interpretations.)

1: “she didn’t feel bad about her actions”

Yes she did, She felt wrong about it multiple times throughout the time she was alone with the main villain. Cassandra did show doubt multiple times throughout the time when she was chasing down rapunzel it just wasn’t outright stated, it was instead shown in body language.

2: “she didn’t have a reason to turn evil”

Well that’s because she didn’t “turn evil” She was manipulated, she spent her whole life dealing with repressed feelings of abandonment and lack of self worth, she felt that she was only worth something if she managed to accomplish something. constantly striving for her adoptive fathers approval, she was put into a vulnerable position when the main villain revealed she was abandoned by her mother for rapunzel, and naturally as a human brain does she searched for someone to blame. not wanting to blame herself she was convinced by the main villain that it’s rapunzels fault and that destroying her would fix it all.

Cassandra never actually wanted to hurt rapunzel she just wanted to feel better and didn’t know how else to deal with her emotions, the villain opened what was seemingly an escape from these emotions.

4: there’s actually a message Behind her arc!

even if anger feels safer it’s just as manipulatable as fear and sadness, the villain uses this to its advantage.

And yes obviously this is childish but that is EXACTLY what trauma does, it stunts your mental growth especially when it comes to emotional regulation and problem solving.

(Cassandra was also a queer coded villain I believe this was even confirmed. she had feelings for rapunzel and it was frustrating to her since she knew rapunzel would never love her that way. This also could trigger her trauma response and she may have been concerned that if rapunzel and Eugene got married she would be abandoned by rapunzel aswell. Though this last bit is just me theorizing. )