The crown prince literally has not had the chance to really help. He helped her already. By explaining what happened to her sister, he doesn't really have the power to get into their business because they're a neutral family, and they don't support him nor do they support his brother. And how is the female lead annoying? When all she has done is explain that she is not her sister, then figure out who her sister is and what happened. Of course, she wouldn't treat her family as her family when she grew up, not knowing them. She was a toddler the last time she saw them. Besides, what her sister needs isn't revenge but someone who is there for her, like the FL is doing even if they don't know each other, and like the story says, Arke is both the victim and the perpetrator. And you might say she did stuff because of the situation, but it doesn't change that she did some things as well.
hays one of the cringy story again, and the ML is just nothing but a face lol. FL is annoying. Arke should have been the mc and take revenge on everyone.