Grace was aware that quite a few violent activities transpired behind closed doors amongst her Supernatural betters and so was not overly surprised to hear that Leo had been a fighter of some sort. Master Quincy had never been one for such displays, offhandedly waving them off as "barbaric." Thus, that was all she'd known of the affairs, and so she didn't need to feign interest when he spoke of the subject.
"I don't picture that being a pleasant upbringing," she said, interested in hearing more but of course not so interested that she'd probe without question. "Forgive me for mentioning it if the subject is a painful one."