The main similarity between the two of them is that both are open to murder and neither has any moral problems with it.
In “The Laboratory” the narrator describes how she is going to kill her lover’s mistress.
NOW that I, tying thy glass mask tightly,
May gaze thro' these faint smokes curling whitely,
As thou pliest thy trade in this devil's-smithy--
Which is the poison to poison her, prithee? (poem hunter)
Compare this to Lady Macbeth’s description of killing Duncan.
Come to my woman's breasts,