The two Power Swaps are actually quite clever, the first having sufficiently weakened Sierra prior to her outburst that she didn't send the whole mountain crumbling down, and the second now causing some of those streams of magma and ice to run dry. Her overactive strength was both fueling her uncontrollable powers and the damage she was inflicting on herself... To some extent, it was also a factor in her self-control, but the mitigation of her power certainly made things more manageable, even if she felt her grip weakening

In the meantime, the continuing Heal Pulse certainly doesn't hurt in keeping the pain at bay.

Kuzuryuu's Air Slash very possibly would have resulted in terrible things had those earlier Power Swaps not happened, but now, the effect released as she is cut out of the earth is akin to being caught in an Icy Wind and a Fire Spin. Painful and irritating, but hardly deadly.