She might love him, she might like him, she might just be after "his fine, tall person," his rank, or his money, or some combination thereof. Please correct me if I am wrong, but I don't recall that we have any indication of which in the novel. And while we all suspect Miss Bingley has been after Darcy for some time, I think we only have hints of it from her behavior towards him, until we learn in Chapter 10 that she is jealous, desires to get rid of Elizabeth, and that "she often tried to provoke Darcy into disliking her guest." She is jealous of his attention to Elizabeht, but does that tell us anything other than she wants that attention for herself?