She is a “quiet” and “modest” representative of the criminal world (meaning: she’ll shoot you quietly and modestly if needed), ready to use any methods to achieve her goal and to play by no rules.
He is a truly bad guy: he prefers to bury his enemies (meaning he doesn’t like to leave traces of crimes), an ideal, impeccably wonderful monster surrounded by traitors and killers—one who simply doesn’t care about any rules at all.
There’s no room for love in their lives, but something clearly went wrong with their first meeting.