[@thewizardguy], just a point: Weakness is complete nullification of power, so something that would render her incapable of sending anything to the void, and presumably be unable to be sent to the void itself. Living flesh being more difficult to transport is a quirk of the power, not a weakness.

I'd assume her weakness would be something those who experimented on her could get fairly easily, to keep her in check. Pure iron? A magnetic field? Glass?