Rage
Her focus for it over the years had always been the inanimate, fences kicked, walls punched in an effort to release her from the hellfire building within. It was her way of coping with long suppressed emotions begging for liberation, the pain helping to repress them until the next eruption.
When Virgil tried to tame an outburst and received a purple adornment to the eye for his trouble, it was time for her to master the beast within.
Each belt earned a little more, yellow had her swelling with pride, the journey towards control and self-awareness rewarded with black.