Canon doesn’t actually say one way or the other as far as I know. I made Kyoko Sun because evidence says that these things run in the family (Gokudera, Bianchi, Belphegor, Rasiel and Every Sky Ever) and Hana is Mist because.
Iirc in the manga Reborn shot Kyoko with a dw bullet and she showed a mist flame
I know she was shot with one but I’m gonna need proof on the fact that it was Mist flame she produced.
i wrote a thing about flame types here, but basically:
people can have more than one type of flame–in canon Gokudera, who is predominantly Storm, also has Rain, Lightning, Cloud, and Sun in order to use Sistema CAI
so it’s possible (probable, actually) that Kyoko has both Sun and Mist flames
[[personally i headcanon that women are more likely to have multiple flame types which explains why (besides blatant sexism, that is) there are so few female Guardians–because they don’t have a predominant type so much as a more stable blend of flames, and thus can’t be the (insert flame type here) Guardian]]