It is easy for the modern reader to dislike Sue, even, as D. H. Lawrence did, to make her into the villain of the book. (Lawrence thought Sue represented everything that was wrong with modern women.) Jude, as well as Hardy, obviously sees her as charming, lively, intelligent, interesting, and attractive in the way that an adolescent girl is. But it is impossible not to see other sides to her personality: she is self-centered, wanting more than she is willing to give; she is intelligent but her knowledge is fashionable and her use of it is shallow; she is outspoken but afraid to suit her actions to her words; she wants to love and be loved but is morbidly afraid of her emotions and desires.
In short, she is something less than the ideal Jude sees in her; like him she is human. She is also a nineteenth-century woman who has given herself more freedom than she knows how to handle. She wants to believe that she is free to establish a new sort of relationship to men, even as she demands freedom to examine new ideas. But at the end she finds herself in the role of sinner performing penance for her misconduct. As Jude says, they were perhaps ahead of their time.
If she is not an ideal, she is the means by which J tide encounters a different view of life, one which he comes to adopt even as she flees from it. She is also one of the means by which Jude's hopes are frustrated and he is made to undergo suffering and defeat. But it is a frustration which he invites or which is given him by a power neither he nor Sue understands or seems to control.