Sana Rae left Voss something they never do.
Sana Rae sent Arcann to a place where Darth Null has been.
she dragged Kira back to a place where Darth Null has been and went off alone with Kira.
she sent Scourge to check out other ruins, most likely a Darth Null site
when Scourge and Kira rejoins our group, we meet them close to Sana Rae
the fact she offers to help Arcann, at a site only she knew anything about.
to me it just seems to add up to her being Darth Null