Additional evidence 会是什么？

我女儿的工卡申请UPDATE是这样说的：
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会要求什么 additional evidence 呢？她今年十八岁，刚上大学。