Applied for I-130, can I apply for B2 visa extension?

[adp]

My mother came to US back in Nov 2019 and her I-94 will be expiring on May 26th 2020. I've applied for I-130 and I've received the receipt notice. At this point can I apply for I-539 - for extension of stay? I could apply for I-485-AOS but we don't have her birth certificate. We are trying to get Affidavits and Non availability certificates but it may take some time.

My questions:
1) As we have already applied for I-130, can we apply for extension of stay?
2) What happens to her status, if in case we haven't filed for I-485 before May 26th and her application for extension of stay got rejected (because of pending I-130 Application)?
3) Can we apply for I-485 without Non-availability of Birth certificate? Will the application be rejected? Or will I get a RFE to provide the documents?
4) Also, what happens to her status if I apply for I-485 and say for some reason they have to reject it? Will that be considered overstay?

TIA!!

[newacct]

She should NOT apply for Extension of Status. First, she doesn't need to and it's a waste of money. Even if she goes out of status, she remains eligible to file I-485 no matter how long she has been out of status. And second, applying for Extension of Status would require her to lie because B2 extension of status requires a statement about her plans to leave, and she doesn't plan to leave. She should get documents ready for the I-485, and file when she is ready, no matter if it is before or after her I-94 expires.

[adp]

Thanks for your quick response!