She can be calmed down from this form but its super risky and best to leave her be until she tuckers out and reverts back on her own. ie Waking back up.
Fighting her is the worst option. Her vital eye is deep within the form at that point and the more stress, the more fury.
Another perk of Kasumi's mutation is her insane healing factor. Being sliced in half, and other severe damage does not actually phase her. Its only when the "Vital eye" in her back is ruptured when she's at risk of fatal damage.
