Complex sentence: While an operative of Syndrome, she presumably was involved in the deaths of several superheroes and had full knowledge of his plan to wreak havoc upon the city; yet Mirage is appalled at the thought of killing innocent children.
Split into simpler sentences: While an operative of Syndrome, she presumably was involved in the deaths of several superheroes and had full knowledge of his plan to wreak havoc upon the city. Yet Mirage is appalled at the thought of killing innocent children.