I believe they took some artistic liberties for the show. The version I'm familiar with goes like this:

"...Then they (the Orsi) having taken her children by the hand, did with a knife make pretense of slaying them in her presence if she broke her word with them. But the dauntless Countess, with unchanged countenance, gazed at them defiantly, and lifting her skirt said to them: ‘E non vi pare egli, stolti, ch'io abbia le forme da farne degl altri?"" (roughly translated, "And do you not think, fools, that I have the molds to make more?") Source