I met a lady in the meads, Full beautiful, a fairy's child; (lines 13-14)
These are the lines in which the lady is first introduced. She's in the "meads," or fields when he meets her, and she's "full beautiful." The final description is a strange. Why does he call her a "fairy's child"? Sure, this is a fairy tale, and the lady is possibly a fairy, but why a "child"? The knight seems to infantilize her, or to treat her like a child in a condescending way, right from the get-go.
Her hair was long, her foot was light, And her eyes were wild. (lines 15-16)
This description breaks the fairy lady into her component parts, telling us about her "hair," her "foot," and her "eyes." It's like the knight is dissecting her with this description.
I made a garland for her head, And bracelets too, and fragrant zone; (lines 17-18)
By placing the "garland" of flowers on the lady's head, the knight is symbolically crowning her as queen of his heart. But the "fragrant zone," or flower belt, that he puts around her waist suggests that she's queen of other parts, too.