Thanks a lot. one more question:
"So my mom just needs to take the old expired passport for the interview. Nothing else, right?
-Yes plus all the documents needed for the visa application such as new passport, photos, payment receipt, etc."
Does mom need to take anything else, like 工作證明, 房產證, 銀行存款,醫療保險, etc, like what she did for the B2-interview the very first time?