Ahh, ( ̄∇ ̄"). So, she's the Fourth Child, Fourth in line, hence she's the Fourth Princess.
But, if we were to distinguish between the male and female heirs, yes, she's the First Princess.
However, she's not the heir of the empire and she's not born before or right after the First Prince[who's most probably the likely crown prince/ grand prince/heir candidate], so MC is given the title of Fourth Princess as she's the Fourth royal kid.
And so she's also in complicated position because of the curse of nardival [?], she's less likely to be an heir.
(≧∀≦)I hope I helped you, instead of confusing you. ヾ(❀╹◡╹)ノ~
There's only 4 kids that the royal couple have.
The first prince and second prince is away with their studies and training. The third one returned from author-knows-where when MC met Reina for the first time, where the honey badger bit Reina episode.
MC live with the third prince at the arena palace.
The oldest two haven't met her after the sword selection.
٩(๑❛ᴗ❛๑)۶ (=・ω・=)ヾ(❀╹◡╹)ノ~
Am I the only one wondering where are her siblings? I mean she's the 4th princess so there must be other princesses and princes so where are they? Are they just not interested in her because they know she won't live past 18 years old, so she won't be a threat to their future?