Additional evidence 會是什麽？

我女兒的工卡申請UPDATE是這樣說的：
Current Status: We mailed you a notice requesting additional evidence.

On October 2, 2007, we mailed a notice requesting additional evidence and/or
information in this case. Please follow the instructions on the notice to
submit the evidence and/or information requested.

USCIS會要求什麽 additional evidence 呢？她今年十八歲，剛上大學。