Butler's the first one I thought of, too.
Isn't Isabel Allende a Latina? She wrote a YA fantasy trilogy a while back, the Alexander Cold books. Not epic, though - more about hidden corners of magic and mysticism in the modern world.
For white authors with black characters, Lee Killough wrote a good (if a little hard to find these days) fantasy in prehistoric Africa: The Leopard's Daughter. I don't think there were many, if any, white characters.
Tad Williams had black MCs in his near-future VR-based sci-fi Otherland quartet; one of them is among the last of the African Bushmen to have any recollection of his culture.
James S. A. Corey's Expanse series is fairly multicultural/multiracial, and it's painted on a big enough scale I'd call it epic, though both authors behind the pen name appear to be white.
Middle grade's probably too young for the kid, but Rick Riordan's The Kane Chronicles stars biracial siblings, one of whom openly talks about how he has to act differently than his lighter-skinned sister because of how he's treated. Also in MG, the star of Wade Albert White's The Adventurer's Guide to Successful Escapes is a black girl.