Board Thread:Theories and Speculation/@comment-1512913-20161122142914/@comment-1732320-20161122225519

Elveonora wrote: Most likely a female from the main family is a princess to the clan. Just like Kaguya was princess of Otsutsuki Clan, Hinata is also a princess of Hyuga Clan, the heiress, even though she gave up the position and it's Hanabi now. The Otsutsuki were able to sense how pure a Byakugan is, so they were likely able to tell that she has to be from the main family according to the pureness.

Well I'm not sure about the "pureness" factor since there's no evidence to support the fact that branch family is any less than the main (Neji for example) but I am also of the mind that Hinata is called the "Byakugan Princess" because of her birthright more than anything else. Even though Hanabi is named the heiress, that wouldn't negate that.