The Thirteenth's time line flow (POSSIBLE SPOILERS)

[Rannie]

Seeing how both Cyella and U boy are both dead by the time Elidibus plucked them from the 13th they can live for ages as they are at this point akin to Ascians. From what they have gone about was Igyeorm was responsible for the whole void and it was their first attempt at trying to cause a rejoining and failing spectacularly.

The whole thing with the Oracle of darkness is a bit different. I dont remember then equating those things with her as voidsent but I could be misremembering it.. id have to recheck that cutscene honestly.

Edit: also it doesn't seem that implausible that the Eulomorans couldn't remember one haughty, over bearing (to begin with) spoiled child. They all were pretty much like that so she most likely blended in.