Well, most discard outright the probability of Maria having anything to do with most of the things in the plot but I still believe she held a pretty big spot in it. At least till episode 4. As I've said before, Maria is the most symbol heavy character in the series. Either these things where unintentional or they had some sort of meaning behind them.
First thing is her name, a clear allusion to the christian faith. Its even written with a cross in it. Depending on which language you use to try an pinpoint its meaning it either comes out as bitter, sea of stars or love.
Second is her attire, she wears dark clothing on top and wears a black crown. In a series where chess plays an important part in its metaphor this seems to point at something but it still sounds like a stretch. What about that weird seating order that the Ushiromiya's have? Anything peculiar with it? From what I remember there are 6 rows of people eating at the table, there are 8 rows in chess. If you discard 2 rows in chess , the two with rooks (what would a chariot or tower eat?), what does that lead us? Where is Battler sitting at and who is in front of him?
Third her eye colors. Everyone else in rokkenjima has dark eyes while Maria has blue eyes. From what my eyes could see, this particular shade of blue is probably "royal blue" which in itself is peculiar.
http://en.wikipedia.org/wiki/Royal_blue . Notice anything about the second, more modern shade? Its a lot like the witches eye color. Also its an allusion to the coming of a king.
Her flower at the start of the series and that plays a somewhat important role in the first 4 episodes could be seen as a metaphor for herself, or Ange or Yasu really. At least thats how I saw it after hearing about of one the stories in the diary.
There are probably more that I cant remember, all of these are circumstantial and could be red herrings at best on RK07s part or he was oblivious to them.