I imagine we’ll find out at the end of this season. Current theories on the forums are. Savvie is trying to free herself from the worm and then will die in accordance to the steps outlined by the Speaker. Essentially self sacrifice makes you worthy for the light. So she’ll become an Arisen (aka Guardian) From there… the theories branch off. Some say the guardians and ghosts we see in the trailer are ina weird place. So that it’s likely Savvie’s throne world. That maybe she can only resurrect the ghosts and thus guardians there where she has some control over the laws of physics. Others suggest her studying of the cabal anti light tech, combined with necromancy she learned from Nokris, will let her do these feats in the “regular” world. And that the weird place is just a new location on some planet. As for the ghosts. It could be she used the dead ghosts and ghost parts that Spyder has been collecting since Forsaken. So she will have some corrupted ghosts that she controls.

That would probably be explained through Lore cards or WQ campaign itself who knows Personally i like believing she somehow got an idea of how to create her own version of the light because of Sagira but who knows really