No, sadly it isn't. She is a random Amazon champion. I'm not sure why this annoying change was made but it was. I think the reason is the Daddy Zeus origins of Diana they couldn't figure out how to make them twins if they are non-clay which is laughable. They could be twins born the traditional way and Hippolyta had dark-skinned ancestors at some point thus the recessive gene (which is a real thing like eye color or hair color) -
"Nubia
After DC Rebirth and Infinite Frontier, Nubia is featured in a backup story in the series Future State: Immortal Wonder Woman.[7] This depicts Nubia in Man's World. After "Future State" and a new version of the Multiverse were created, this version of Nubia is reintroduced as an Amazonian champion tasked with guarding Doom's Doorway, a hellish portal on Themyscira. Nubia shortly becomes Queen of Amazons when Hippolyta returns to Man's World to represent Diana in the newest iteration of the Justice League.[8] After returns to the living, Diana officially blesses Nubia to share her title as Wonder Woman, in addition to her new role as Queen.[9] While Nubia is no longer Diana's twin in a literal way, the two were both born on the same day and fostered a close sister-like relationship. Nubia is also shown as having a romantic relationship with the Amazon blacksmith Io.[10]"
https://en.wikipedia.org/wiki/Nubia_...0relationship.