I take it you are refering to the first section of this great novel, in which Chapter Seven is entiteld "Queen of Night." This chapter is key in building up our impression of Eustacia Vye, especially in terms of her appearance and character. Consider the way in which she is described as being "the raw material of a divinity" and she is explicitly compared to a "normal woman" as we are told that she has the "passions and instincts that make a mortal goddess." Her hair in particular is given particular mention, as it "closed over her forehead like nightfall extinguishing the western glow." At every stage, her appearance is contrasted to other young women around her, and she is thus identified as having a singular appearance that speaks of mystery and of "pagan" beliefs and passions.
Perhaps the most revealing comment regarding her personality comes in the following quote, that points towards the way in which she is a bundle of contradictions and different ideas:
Thus it happened that in Eustacia's brain were juxtaposed the strangest assortment of ideas, from old time and from new. There was no middle distance in her perspective—romantic recollections of sunny afternoons on an esplanade, with military bands, officers, and gallants around, stood like gilded letters upon the dark tablet of surrounding Egdon. Every bizarre effect that could result from the random intertwining of watering-place glitter with the grand solemnity of a heath, was to be found in her. Seeing nothing of human life now, she imagined all the more of what she had seen.
The past thus exerts a curious fascination on Eustacia's character and indicates that not only does her phsycial appearance make her something of an incongruous individual, but also her character would have been better off living in a different time and a different place. The overall effect of the description we are given of Eustacia's character in Chapter Seven is thus to highlight how extraordinary she is as a character and how she really does not fit in to her surroundings.