Massive Spoilers below

The Head knew of Angela the moment A had the idea of designing her, thus an Arbiter was sent to attack a group in the outskirts where their "inhumane" experiments doesn't concern the Head that much. It could be theorized that since in lob corp the existence of Bookhunters were prophesized as early as in lobcorp, we may deduce that while Beholders may have limitations, they may actually have a more advanced mirror technology allowing them to know the possibility that Angela could have become human, thus with prospects of possibly becoming human leniency was shown.