Oooh Theories! Ok so my theories. Madame X is stronger than all her Pokemon combined. She is capable of using a sword and doesn't need the use of her pokemon. She has access to the legendary Pokemon of destruction, Yveltal. My first thought was Griselda since she seems the warrior type however, imo she seems to give off the aura of having Giratina as shown through her events of opening the treasures in wispy path. So I don't think its her, but I could be wrong because she has black hair and maybe red eyes?
Ok Nora. I thought it was Nora also because seeing as her soul was erased by accident. Honestly this is still up for debate as we have yet to meet or see her, for ourselves. Although in WLL it looked as though she was turned into stone when the hooded pokemon pushed her and Taelia to their deaths and only Yveltal is capable of doing so, but if that's true how did she survive? Again, up for debate. (BTW you put Nora's name twice for votes)
Now we go to one of my favorite people, Melia/Marianette and yes I'm using both blonde's in this. So Marianette, I can't come up with theories for this since Madame X approached her way back when so that's out. MELIA. Ahh Melly Belly. Sooo something about her I find extremely interesting. Team Xen is after her because of the light inside her that's been somewhat established. She is able to purify/bring things to life possibly using her power as seen in v10. So based on what we know from Pokemon XY, Xerneas the pokemon of life is able to bring people, plants, pokemon to life if you aquire it. Yveltal the pokemon of destruction able to destroy/turn people and pokemon to Stone. What does this stand? Madame X weilds Yveltal, Melia possibly weilds Xerneas or Arceus via her Golden light. So what does this tell you? Personally speaking Idk who Madame X is. It could be anyone, or someone we may have come across. But I'm guessing either Nora or an evil version of Melia who has lived through the same hell that storm 9 has inflicted and is in an infinite loop of failure. This my theory!