I haven't gotten up to that point myself, but considering that Ciel's a Flying type gym leader, sounds like having either a Steel or Rock(especially) type would help out, I mean unless she's got something with her pokemon to counter them like Fighting or Grass. Though, you did mention that the Mega Altaria has Earthquake which could be a problem.
Aggron or Gigalith would be a fine choice to have in your rotation, in my opinion, but of course it's up to you. Solrock/Lunatone could also be helpful since that eliminates her from using Ground.