Strange, that I have a bit different feeling about her. I mean, I condemn her pervious deeds, think that she is/was a very spoiled brat and would not trust her, yet, somehow I'm perceiving her as 'worthy opponent'. Probably because she is using her head more than other characters. She knows, that she is in low position compared to rest of the girls (yes, she was forgiven, shamed etc. and technicaly has a 'clean card', but in reality, she is still in the bottom of hierarchy), has got enemies (Yuki, Alice for example) that are superior to her in straighforward ability to harm her. But, her nature is pushing her to raise again and get, what she wants, feels she deserves. She is smart enough to know, she must be cautious, she needs to learn a lot about the island, culture etc. But she decided to join the chessboard and, eventually, win.I echo the sentiments of others regarding Sarah, and as I said before, I rarely lose composure, but I found myself with a burning desire to mentally, emotionally and physically break her before throwing her into a pit to die, whereas before I would've been content to let her fall off the cliff (I tried, and it wouldn't let me). I truly despise her, regardless of signs of what I predict will be a redemption plot, and in my view, the MC of the story is a complete imbecile for allowing her to live at all
We shall see, if her character will be tempered by patience and experience, but I think it would be a great disservice to her if she would get a classic redemption story - that would make her a 'good' girl. I think she would be much interesting, if she would stay in 'grey' area, by her own choice.
And looking on the other girls - who could rival her in using mind? I think that Leah, while beeing highly competent (excelent manager, organizer), has no imagination, ability to think outside of the box. She lacks of wider vision of things. Yukihas got too narrow horizons to think wider and I'm not sure if intensive education can change it. Alice and Sonya are predictable and not that much creative by their own. For now, only Hazel seems to be able to challenge Sarah, yet, somehow I think she will not be able to keep up in the longer run. Oh, and we have Scarlet, who seems to be also intelligent, yet is too constrained by her character for using its full potential. Daisy is... not too interested in such 'down to earth' things.
And to be clear, it doesn't mean, that I don't like other girls. I just have a feeling, that if one of them would become an enemy/rival, Sarah would be the most dangerous one (has got most chances to win, to get what she would be planning while facing oposition).