B2 Visa extension no response- How long can We stay?

Hi, I applied for my mom b2 visa extension. My mother’s I-94 expired in June 6, 2020 and no response on extension application as well. 12 months getting over by Dec 6, 2020.

How long should we wait for response on extension?

Can they stay till we get a response or should we file our 2nd extension?

Someone said we can stay for 295 days after filing extension but not finding any such rule mentioned anywhere.

Any help please