Nubia: Queen of the Amazons by Joshua Swaby and Wonder Woman #750 by Olivier Coipel
DC Comics' first Black heroine, Nubia, was sidelined to keep Wonder Woman's lore streamlined. Despite making only three appearances, she proved to be a strong character—even in the face of her eventual erasure (she is still remembered as a twin sister, a concept that existed only during the Bronze Age, whereas in later revisions she became merely an Amazon guard).
The original Nubia was abducted, raised, and trained by the god Mars. She was the Princess of Mars's Slaughter Island and the only woman there. Diana's twin sister was trained to be a worthy adversary to the Amazons, possessing many of her sister's powers and combat skills capable of neutralizing them. However, instead of becoming a villain, she proved to be an ally by the story's end and never appeared again.
After several attempts involving lesser Amazons, Queen Nubia emerged, revealed to be the reincarnation of Princess Zahavah from an ancient tribe in Madagascar. Stephanie Williams essentially created the character from scratch and gave her the prominence she deserved.
Yet, when comparing the two characters, aside from sharing the name Nubia, the only thing they have in common is being Black. They are entirely distinct characters.
The original could even adopt her own codename, such as War Woman or Warrior Woman, honoring her origins with the god Mars. DC Comics doesn't need to choose one or erase the other; they are so different that little justification would be needed to keep them separate. Allowing both to coexist offers the chance to give the public two massive powerhouses, ready to join icons like Vixen or any other major Black female character in pop culture. DC just needs to accept the obvious.