I'm fairly sure you're right, but what I meant by that disclaimer was that should one of the 4th Q. figures turn out to be Sorceress or Mara, that would mean there was overlap between the three facts. (I suppose it depends on if you consider the Sorceress as part of the Masters.)
But I don't think it will happen that way; personally I think the 4th Q. female is from POP, probably Frosta or Glimmer.