Rena (the Windbloom king's Otome) replaced her daughter with Arika (the real princess because she has the sapphires). That does not imply that Mashiro is her real daughter. Mashiro was presented as the princess by a minister, now deceased, which is why so many people suspected that Mashiro was not the real princess.

Her real daughter is most likely Nina. Which explains Nina's old memory of Rena smiling at her.

Mashiro is just, Mashiro. I'm sure there's more to her than that, but they've implied nothing yet. (Not counting the whole Organ thing.)

All an elaborate plot to keep the real princess safe from harm. Kinda harsh on her own daughter though...and we know Nina ended up with a pretty harsh childhood. It's weird though, you can't possibly deny that Rena and Arika look exactly alike. I suppose that could all be a ploy by the writers so we wouldn't suspect, but its unmistakable.