[The Saucepan Man]

Originally Posted by Lalwendë

She is not Valar or Maia, as she did not come to Arda when they did, and she is not of Arda, as the text states she descended from the darkness.

While I tend towards the theory that she is not of the Ainur, I don't think that we can definitively state that Ungoliant was not a Maia. The "darkness that lies about Arda" could still be part of Ea, the Universe, in which Arda lies, and which was created by the will of Eru. A Maiarin Ungoliant could therefore have entered Ea after it had been created and subsequently descended to Arda after the establishment of Manwe's kingdom.