8老师：
我母亲以前曾经在美国帮我带孩子，一带就是5年，没有办理延期，就这样黑下来了。后来她就回国了。
前几天我母亲到广州做绿卡visa interview。领馆要求提供"Evidence of legal 5 year stay in US"。这该怎么办啊？
-Obviously she is unable to provide such proof because she does not have it. Your mother unlawful presence in US was > one year, so she is subjected to 10-year bar, and that means she cannot get any visa (including immigrant visa) to enter US within 10 years from the date she left US. So, she may just tell the US Consulate she has no such proof, and then the US Consulate will deny her immigrant visa application, or she may just withdraw the visa application.
You can sponsor her immigrant visa again after her presence in China is for 10 years.
