There are threads about the theory of the fourth piece of the triforce which is either called Quadforce or Tetraforce (I prefer tetraforce) and one of the most important things to that theory is that there has to be a fourth goddess for the fourth piece. If you believe the theory, that statue could be the goddess. Throughout the people who believe in the theory, some people believe that the fourth piece is an inverted triangle that fits in the center, while I've also heard that the fourth piece could actually be the triangle that appears when all the pieces come together to make one bigger triangle. I prefer that theory.
In that theory, the fourth goddess helps the other three work together to work correctly.
Another good argument for that particular tetraforce theory is that in TP, there is a goddess for every province except for the Ordona province. Lanayru=Nayru; Eldin=Din; Faron=Forore. Ordona=? Ordona is also a combination of the three goddesses names Or=Farore; don=Din; na=Nayru. All the provinces sound like their goddess so Ordona probably sounds like the name of the goddess that's responsible for that light spirit. If the fourth goddess is responsible for Ordona, and also the fourth goddess helps the other three work together, then I think it would make sense for her name to be a combination of the others' names.
Also, that makes sense that the fourth goddess would look like a combination of the other three too.
Also, in ALttP, at the end, Link makes his wish to the triforce, and a voice speaks to him calling itself the essence of the triforce which I think is the voice of the fourth goddess. Maybe when the 4th goddess helps the others work together, the 4th goddess speaks for them.
Anyway, what I'm trying to say is, I think that the goddess in the statue is a combination of the three goddess in a way, but also the fourth goddess.
(If you haven't noticed, I sorta believe in tetraforce theory.)