on the one hand, I really dislike it when people play with the feelings of others, on the other hand - go ahead, girl, go ahead, give them hell. First destroy that "best friend", then dump your fiancé bastard in the best way possible! (Also, it's not like he ACTUALLY has feelings for her, anyway)
Also, very obvious she'll end up with the duke, mostly because he's not focussing on her appearance, but interested in her as a person and actually stands up for her, unlike Hui.
And I'm all for it - decent men with backbone are always a win.