A moderately sized flat disk just above her heart area plainly visible to most.

The whole thing is a defibrillator, built and attached out of her mistrust of her artificial heart and acts as in it's name as an emergency power source. The sphere in the center is filled with highly conductive elements atomized to power the heart in case of slowdown or failure. The filled spaces near the sphere serve as individual meters to measure available power left for consumption, draining from top to left, right, and then the bottom.