This Bible contradiction is from the Skeptic's Annotated Bible.
Yes, she had faith.
Hebrews 11:11 View context
Through faith also Sara herself received strength to conceive seed, and was delivered of a child when she was past age, because she judged him faithful who had promised.
No, she laughed at God.
Genesis 18:10-15 View context
And 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.
Now Abraham and Sarah [were] old [and] well stricken in age; [and] it ceased to be with Sarah after the manner of women.
Therefore Sarah laughed within herself, saying, After I am waxed old shall I have pleasure, my lord being old also?
And the LORD said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old?
Is 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.
Then Sarah denied, saying, I laughed not; for she was afraid. And he said, Nay; but thou didst laugh.