My mother entered US with a valid visa in June 5 and got 3 months stay (until Sep 5) as per I-94. Her visa has expired 2 months (Aug 5) after she entered in the US and now we're planning to file for I-94 extension but we're not sure if the visa should be valid (not-expired) for I-94 extension. Can someone please advice?
Once she is in USA, her stay is governed by the I-94, not the visa. There are other issues with extension (such as future problems in entering, etc.), but visa is not an issue.