The quicksand isn't deep enough for her to be completely submerged... just enough to confine her up to her chin. Ed adds another set of stone walls for extra measure.

With April confined by the alchemical quicksand, Cipher Nine focuses on Ember, firing more stun blasts at her in a steady, measured rhythm, hoping to keep her disoriented long enough for them to cut April off from her voices. "They're occupied," he calls to the others. "How do we cut April off from her voices long enough to take care of Maloker?"