It’s not TJs sister or a Riptor clone is all we know. The only sibling it could be other than Maya is Cinder’s sibling seeing that Hisako and Kan-ra are too old to have any siblings left and Aganos is a statue.
Im also wondering if Mira is just her sister or identical twin. If identical it would be cool if they change her face so it looks like a vampiric version of her