I think the "usual" approach would be making it an Aspect and working through Compels.
I'd replace Cascade of Sensation with something along the lines of:
Psychic Feedback. Whenever you are in a fight and another person, or anything that is capable of feeling pain, takes Physical Stress you suffer from an Mental Attack with the same amount of Shifts, resisted by Discipline/Conviction (Not sure which one is more apropiate).
Since 2 refresh is a lot of refresh you might even want to add:
Your Defense is negatively modified by your Empathy.
This system would restrict your combat skills less (In Changes Molly didn't seem very impaired by the mayhem around her when she did her One-Lady-Rave) but would lead to neat Consequences (Like the Extreme one: "Ragged Lady"
)