Harley was dragged into underground fighting by her ex and stuck around for the money. While her nights are devoted to a muggy arena full of others waiting to try and rip her apart, her days are spent in the company of her best friend or sewing. She dreams of being a seamstress full time, not having to rely on fighting to pay her bills.
Part of her right ear is missing, while her body is littered with scars from being in the ring for so long. Unless your character is extremely close to Harley, don't bring it up, don't mention her ear or talk about her scars. It's a sure fire way to make her uncomfortable or lash out.