What is going on with Cressida?

I'm very confused to the way this is written. For the past 2 seasons Cressida was a cruel bully. I didn't like that they made her so stereotypical (Blonde white girl), but I was like "Okay this makes sense I guess, and it gives some more depth to the way Penelope feels."

Season 3 is where I think they poorly wrote her. Why take all the time and effort to give her a character arc and make us feel bad for her only to turn her into a "villain" in the end? We got more insight into her character, she softened up with Eloise, she became much kinder, she protected Eloise's secrets, she left Penelope alone, she was being forced to marry a guy 3 times her age, etc.

The audience is left feeling sorry for her and I personally was rooting for her to get the money and run away. But then all of a sudden its like after she announces she's lady whistledown, it's supposed to make her a villain? What annoyed me the most is ELOISE who knows that Cressida isn't Whistledown still treats her like crap and pretends like she's Whistledown even though she knows what a horrible situation Cressida is in. Like I'm sorry whatever happened to caring about women's rights Eloise?

And no this isn't a case of feeling sorry for a villain just because they have a sad back story. Its a case of they took a mean character, gave them a redemption arc, and then all of a sudden just turned them into a villain again for convenience.

Edit: So I'm seeing a lot of comments excusing Cressida's mistreatment because she was a mean girl in the past. To that I say, why does Penelope get a pass? Hear me out. Penelope cowardly writes about everybody's business, often times in such a way that it directly harms the person's family, their reputation, and their life. Sometimes she even does it because of lingering jealousy or resentment. But we all just kind of excuse it because Penelope was neglected by her parents and she's invisible in society and so we feel sorry for her. And I too feel sorry for her and I understand her issues too. But I'm asking why can't we extend that same sympathy to Cressida?