Please advise! My mom now is

waiting for her GC in US, but needs to go back to China urgently for about a month. Her GC watinig time on her USCIS account says in about 4 months. She already got her I131 advance parole aproval letter on hand, what it says valid for 5 years.

Question:

1. My mom's multi-entry visa was expired back to the beginning of this year. As she is in the queue for her GC, that B1 visa is no longer matters, right?

2. How should my mom use her AP? Does she need to show it to the custom officer when she leaves US or just when she comes back to US? It is just a letter, will it be aquired or taken away by the custom officer when she comes back to US? As its expiration date is in 5 years, how many times could it be used? Is it still valid even after my mom gets her GC? 

3. Any other docs/files my mom should carry with her for her urgent trip?

Thanks alot,