Board Thread:Naruto Discussions/@comment-30168027-20170206134841/@comment-4912646-20170206151222

And even then, in the translations I've seen, Black Zetsu says Kaguya "brought out" her Gudōdama, rather than creating one. So it could be that she always has that one but can only bring it out after absorbing tons of chakra, the same way Naruto's only appear while he dons his chakra cloak.