In the poem "La Belle Dame Sans Merci," what is the lady like that the knight meets?

The woman the knight meets in "La Belle Dame Sans Merci" (The Beautiful Woman without Mercy) is a femme fatale. That is, she is a fatal woman. She is beautiful, alluring, and irresistable, and ultimately the downfall of any man who falls for her. 

The narrator finds the knight in a barren land where "he sedge is withered from the lake, / And no birds sing." The woman, then, not only destroys the knight, but the land around him as well. (This is a common motif in ancient myths, such as that of the Fisher King, who is wounded and is thus the reason his realm is a wasteland. The same motif can be seen in Sophocles' Oedipus.)

This femme fatale is "beautiful, a fairy's child" (13-14). She is a lady (not a peasant), and her hair is long and her step is light, meaning she is graceful as well as comely. However, her eyes are "wild" (16); this is emphasized, appearing thrice in the poem. Her wild eyes suggest she has an untamable spirit, which makes her even more irresistible to the knight. When he makes decorations for her from the flowers on the mead, she looks at him "as [if] she did love, / And made sweet moan." She is, then, an alluringly sexual creature. 

He is a gentleman, placing her on his war horse, but he cannot take his eyes off of her. In turn, she doesn't just sit and ride; she bends sidelong and sings "a faery's song" to him. This song, we may assume, has a magical, seductive quality. 

She lives on the mead, and thus finds him plants to eat, including roots and wild honey and manna-dew, all sweet things. (Manna-dew is a reference to what the Lord gave the children of Israel to eat in the Sinai Desert, which implies the knight's lady is a goddess-like figure.) 

She seduces him--emotionally--with her looks, her moans, her songs, her food, and her words, then she weeps and sighs, bringing out the protector in him. Then she lulls him to sleep where he sees the many men--kings and princes--who have all died at her hands and warn him of his fate (she has him in "thrall," meaning he is her slave). 

Despite this knowledge, he shows no desire to leave. 

Perhaps a better question is who is this lady? Is she Love? Or is she, perhaps, War--the "lady" so many men are seduced by and even when they know they will die at her hands, they are powerless to leave her?