Why Did She Laugh?

S 11:69-73 And our messengers came to Ibrahim with the good news. They said: Peace. He said: Peace. And he did not stay to bring a roasted calf. / But when he saw their hands not reaching towards it he felt unfamiliar about them and felt a fear of them. They said: Do not fear. We have been sent to Lut’s people. / And his woman standing and she laughed. Then we gave her good news of Ishaq and behind Ishaq Ya’qub. / She said: Woe is me! Do I beget when I am an old woman and this my husband is as an old man? This is a wondrous thing. / They said: Do you wonder at Allah’s command? Allah’s mercy and his blessings be upon you, household. He is praiseworthy, glorious.

Only HUMAN Messengers Sent to Men

In verse 71 the unnamed Sarah laughs. Why does she laugh? Let's turn to Genesis 18:9-15.

9And they said unto him, Where is Sarah thy wife? And he said, Behold, in the tent. 10And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him. 11Now Abraham and Sarah were old and well stricken in age; and it ceased to be with Sarah after the manner of women. 12Therefore Sarah laughed within herself, saying, After I am waxed old shall I have pleasure, my lord being old also? 13And the LORD said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old? 14Is any thing too hard for the LORD? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son. 15Then Sarah denied, saying, I laughed not; for she was afraid. And he said, Nay; but thou didst laugh. Genesis 18 KJV

In the Genesis account, she hears the good news then laughs; in the quranic account, she laughs THEN hears the good news that prompted the laugh. Hysteron proteron. The cart before the horse.