Hi. My wife and I are applying for greencard for her mother who came with B2 visitor visa in Feburary of this year. The visa will expire by the end of July. We got a letter from Immigration office asking for birth certificate for my mother-in-law. Since she was born in the 1940s in China, there is no birth certificate and it will take long time to get it by asking friends' friends to help. In this case, do I need to file visa extension for my mother-in-law? And if we get the birth certificate after the deadline set by immigration office (I think it was something like 90 days), do we need to file for green card again? Thank you very much for your help.