In the conversation between the Duchess and Antonio that ends with an agreement for the two to marry, the Duchess, at first, does not tell Antonio why he has been summoned. Instead, she tells him,
I am making my will ...
Were not one better make it smiling, thus,
Than in deep groans and terrible ghastly looks,
As if the gifts we parted with procured
That violent distraction?
(I.i.376-381)
Why, would someone bring up death right before speaking of marriage? The two are generally viewed as the antithesis of each other: one ending life and the other marking the beginning of a "new" life. Yet the Duchess, who has herself suffered from death in a marriage, brings up the topic before even asking him to marry her. It's awkward - certainly not a romantic beginning to the conversation - and it's uncomfortable. The language she uses is so vivid and specific that one wonders if this is what her husband went through on his death bed. Readers know so little about him and the Duchess's relationship with him that it seems possible.
The Duchess goes on to explain that if she were married, there would be no need for a will - everything she owns would automatically revert to her husband's holdings. She doesn't consider that her husband might not outlive her, as was the case with her first husband. This seems odd. One would think that since this has already happened to her, it would be a possibility she would address. Perhaps this is simply a part of her wooing strategy. It seems more likely, however, that she looked on the life she wants to start with Antonio as a new start, a beautiful beginning.
The passage can't truly be called prophetic, because, ironically enough, she does not end up groaning and violently mad before her death, though Cariola's desperate casting about for an excuse to halt her own execution could fit this description. She is surrounded in her last days, however, by those who sound as tormented as she would be in the death she envisions earlier in the play. Her own death, she confronts calmly and cooly, as though she is unsurprised by this tragic end to her life.