No specific information given out by CLAMP.

<Alice> What's her title?
<Satsuki> Yil / Masoushi (Sorceror).
<Rei> From the looks of her spells, her element is
      ice.
<Yang> From the conversation with Clef, it has been
       determined that she was Clef's student before
       she turned to Zagato.
<Asuka> And she decided to fight her old master
        purely from her one-sided love for Zagato.
<ChunHyang> So none of this crap would have
            happened if Zagato decided to give up on
            Emeraude and settle for Alcione?
<Asuka> Seems that way.
<Alice> But if that happened, RayEarth would have
        been boring!
<Satsuki> And you want scantily-clad old ladies to
          be happy?
<ChunHyang> It won't matter because she wouldn't
            be a villain!
<Asuka> And speaking of which, she is such a
        dominatrix!  She enjoyed watching the
        Knights get hurt!
<Shinji> But that was only because she was doing
         something that Zagato would be happy about,
         right?
<Asuka> We'll never know about that, will we?