I hope Luna WINS.

Well the dream world is Dra'Meia's element, much like Luna so they're pretty evenly matched I think, While Luna might be stronger with magic, Dra'Meia is physically stronger but in the dream world she can use some strong magic as well so it could go either way. Also Luna isn't aware yet that she's facing another who can physically enter the dream world like her so that might catch her by surpise.

Oh really?

Dra'Meia is a nightmare, as such she can enter dreams and manipulate them, she can even drag things out of a dream and into the real world. She can also feed on fear and become stronger from it. She's not evil, but she's not exactly good either and usually she is summoned by someone and contracted for some purpose in the dream world as she can take things out of them and make them real, or make some one forget about something... It's why she is called the dream thief.

That said when she's not under contract she prefers to just explore people's (or ponies in this case) dreams peacefully and only take things she finds interesting and would have no impact on the dreamer, though if someone crossed her she may also haunt their dreams to feed on their fear and become even stronger or in extreme cases she may also slowly feed on their life force. (she picked up a few abilities from a succubus at one point, so as such she can feed on other emotions as well as life force.)

But as I'm not sure yet where this story might go, time will tell I guess what happens.

Okay then.