It is clear that from the beginning enchantment or some form of magic is at the heart of the attraction that the strange lady is able to provoke in the Knight who is left the worse for ever meeting her. However, at the same time, it is clear that the lady's beauty has something to do with it. Note the way that the knight describes the lady in stanza four:
I met a lady in the meads,
Full beautiful--a faery's child;
Her hair was long, her foot was light,
And her eyes were wild.
Note the way that her beauty and her enchantment are linked in this stanza. She is "full beautiful," in fact so beautiful that the knight concludes she was a "faery's child," or the product of magic. The "wild" description of her eyes combined with the way that she made "sweet moan" also add a frankly sexual element to the attraction. The way she is described and the actions that she engages in suggests that she is casting some kind of spell over the night, as she sings a "faery's song" to him and gives him "roots of relish sweet" and other such offerings to eat. Reference to her "wild, wild eyes" is again made later on in the poem when the knight kisses her eyes four times and closes them.
Thus it is that if we examine the poem the nature of the attraction seems to be in the way that the lady is able to enchant the knight with her beauty and magic. Her other-wordly nature is stressed throughout the poem, and so we can imagine that the knight finds her exotic and attractive.