I can't really blame Luna for being sore, i mean, Celestia says that they are meant to rule together as equals, but she still haven't changed the throne room so that they have equally large thrones? It might not matter from HER perspective, but if a a person with big political Powers arrives to have a meeting with them and see how Celestia's throne is smackin the middle and Luna's at the side of it and being much smaller, of course they will see her as the bigwig with all the Power.

So in short, Move your throne slightly to the side and give your friggin co ruler/sister a bigger throne for Crying out loud!!!!!