That was the kind of person Emilia was; magic so strong that she could prevent such things from slipping through, into places she didn't want them to go. It had its limitations, of course. And some beings could even break barriers, but it would require them to know the barrier was there, at the very least. And, ultimately, their own abilities would have to be stronger than hers.
Adair, Blayze and the others served her, in part, to keep her protected and hidden from the world.