@ninaaziz I agree. We have to remember that she doesn't have the benefit of observing things like us the readers. Her impression is based on his reputation and her own experiences of seeing him as a glaring brooder. For us, we know he is a male lead so we're given an extra dose of confidence that he's a good and decent guy. While it might seem a bit extreme that she thinks he'll kill her off, I think deep down she knows he isn't a bad guy but that doesn't change the fact she finds him very intimidating. In fact I think she's probably more often than not speaking in hyperbole, she may not think he'll actually kill her off but she's still frightened of how he'll react if she gets on his bad side.
The fact is people fear what they don't understand and Cabel is a guy who I think very few really know. When someone leaves a bad impression, you're usually moved to overlook that only when you either have a personal interest in them or if you've been paying attention to their actions over time to realize you were wrong. Renee hadn't yet paid him that kind of attention so she's slow to look past her own bias. While less fitting for a heroine figure, I actually like that we get to see such flaws. She can be a bit foolish, lazy, selfish (though not to an extreme) but that makes her a person rather than an ideal.
I do worry for poor Cabel though when he inevitably finds out about the false confession. Not only will it hurt to find out she wasn't into you to begin with, but it'll be a double blow realizing the only reason she didn't correct the mistake was because she was too afraid of you to do so.