In the practice of hoodoo/rootwork, the term, "lady-hearted", originally referred to a male worker who refused to do bad work or enemy work, that brought pain, harm, suffering, or death to a targeted person. Of course the term means that the male worker has the heart of a woman instead of a man. Keep in mind that when this phrase arose, good, respectable women, even in hoodoo/rootwork, would never mess with anything "dark-sided", or at least that was the public face put forward. Times have changed and women are just as equally performing evil as men are and so the term "lady-hearted" is now used to describe any practitioner, regardless of gender, who refuses to do harm via harsh work.
A similar term also used to describe these people is "faint-hearted"; however there is a slight difference in the meaning between these two phrases. This latter term of "faint-hearted" implies weakness or lack of courage, meaning that the practitioner doesn't have the guts to perform harsh work. The term "lady-hearted" does not come with the baggage of an association with weakness but instead implies a core-personality trait of kindness and empathy.