This is indeed a good example of dramatic irony, one that arises from the difference between what Macduff falsely believes about Lady Macbeth, and what we, the audience, know about her.

Dramatic irony arises when the reader or audience knows something that a character does not. The character is mistaken, or uninformed. We know better, a situation that can create a variety of effects -- ranging from the tragic to the comic.

But whether we find the results humorous or distressing, our emotional responses depend on our ability to judge how much the character's beliefs diverge from objective reality. Oedipus Rex is frequently cited as an excellent example of dramatic irony: The audience knows what Oedipus does not -- that the man he killed was his own father, and that the woman he married is his own mother.

In this case, the audience observes that Macduff is extremely misguided in his belief that Lady Macbeth is a delicate female who needs to be protected from talk of violence. In part, his words reflect a chivalrous fantasy about female psychology: Ladies are too innocent and gentle -- they can't cope with the reality of evil deeds. But it also reflects his mistaken beliefs about Lady Macbeth as an individual. He doesn't imagine that she could have anything to do with the murder.

We know that -- on the contrary -- she is the mastermind behind the murder. It was her idea to drug the king's chamberlains. She is the one who egged Macbeth on. She's the one who coolly framed the guards for the murder by smearing the dead king's blood on their daggers. Far from being too delicate to hear about the murder scene, she's tampered with it--literally bloodied her hands in it--and derided her husband for being afraid to look.

"The sleeping and the dead

Are but as pictures;  'tis the eye of childhood

That fears a painted devil."