You're talking aboit having a "bad friend" (who we know will be the heroine), but you seem to be a pretty shit person, yourself.
So, yeah; the guy made the business decision about engagement, amd that's one thing. But... the fact that you immediately state that you simply refuse to help in any way, and make a big deal about acting like a superficial friend?
Like, you're not interested in actually being a friend, but you're willing to act like one on the surface... and you consider that going out of your way?!
You sound like a piece of shit, lady.
Honestly, the translation is kinda confusing, so I'm not sure which of us misunderstood.
But from what I understand, it's not that she didn't want to help, she just didn't know the right way to save him.
The prince seemed to be hated by the people in the palace, so he was lonely and his heart was empty. She assumed that the role of heroine in the game was to fill that hole. But she never got to play his route, so she didn't know how. Not to mention, she's the villainess. And given how she felt she couldn't help her siblings in her past life, she felt even more unsure about how to save the prince.
But she knew it would suck if the prince grew up alone. So, she wanted to become his friend. She wasn't planning to be someone who can save his heart, but she would become someone he can talk with. At least until the prince meet the heroine.
So yeah, I don't think she's a bad person.