221 g based on previous Port of entry

My wife recently attend H1b visa interview. She got 212(g) with white slip.

She did masters in United states earlier. When she was entering into the united states on F1, at Port of entry they stopped for questioning. US officials got all answers from her and sent her inside. During this process, somehow she got two stamps on her passport with admitted (one with F1 and other with F/E).

Secondly, one departure immediately is missing on her I94 after that.

During H1b interview, Consulate officer asked her about departure missing and she explained. After that she keenly observed those two stamps and did search her records. Finally, she gave a white slip asking for documents related to incident in POE.

We are not sure what documents we will need to submit for this case. She is not given any documents at POE by CBP officials.