Who was Nimue?

OK. Quiz time again. This time only the Corinthian is requested to delay answering for a couple of days to allow others a fair chance (hint hint Mr 'Out to Lunch')

Who was Nimue?

For a contextual reference, try this quote (name the source for double points)

"Is this what Nimue might have felt like when she took on Lancelot as her apprentice? Starting something that she had no idea where it would take her?"

Somehow I have found the quote abstractly fitting this weekend...