SilverWook said:

In the real world, when royals serve in the military, how are they addressed, by title or rank?

That's a good question. But, I think in a situation like this, her "Princess" title would mean very little compared to her rank. Both to the other members of the Rebellion and to herself as well. But, I don't really know.

Also, by addressing her by rank, it would help to flesh out her character even more. I think it would be a nice alteration in a fan edit or a REVISIT-ation of some kind ; )