I believe the DNM is Birgitte. I don't have any references but I do have a theory. I think the DMN is a mythical name. Birgitte was a hero in the Seanchan land and created the name Daughter of the Nine Moons. The Seanchan use DMN as an legend so they would have somebody to worship and look up to. Of course, this would mean Mat would be Gaidal Cain reborn... which I believe he is. Notice in the books that Gaidal Cain disappeared from Tel'aran'rhoid about the same time Mat entered the ter'angreal in Rhuidean and received all his memories. I think all these are Gaidal Cain's memories from his past lives. Of course, this is just a theory...