Board Thread:Wiki Discussions/@comment-1512913-20140521221412/@comment-3568954-20140523092325

Ten Tailed Fox wrote: HagoromoOtsutsuki wrote: Hagoromo is the first (along with his brother to have rinnegan) Shinju been in the narutoverse for centuries Byakugan is the 1st true dojutsu among sharingan+rinnegan

All of that is speculation.

this is just speculation on my part

but i think that kaguya was born with a byukugan and that is why she had it