All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is not permissible to relate such stories that contain disbelief unless the purpose is to deny it and warn people against it because what that woman said is considered as mocking the religion and blasphemy against Allaah, the Lord of the Worlds.
As regards you laughing and smiling in such a case, then this is wrong because you are Islamically required to condemn and hate such statements and relating them. If you did not condemn her story, then you should repent to Allaah; for more benefit, please refer to Fatwa 86527.
As regards uttering the Two Testimonies of Faith and performing Ghusl because of thinking that you have gone out of the fold of Islam because of smiling and laughing without accepting that and without being pleased with the mockery, then this is not required. You are still a Muslim, praise be to Allaah. For more benefit, please refer to Fatwa 132415.
Allaah Knows best.