B2 visitor stay extension

[Rahulv21089]

Hi,
Currently my mother is in US on B2 Visitor visa.
Her I-94 expire on 08/27.
I have submitted stay extension on 06/08/2023 with I-539.
What to do if decision not come by 08/27 ?
Can see stay long after 08/27 or she need to leave before? If she can stay as application is in pending status then how many days she can stay?
If she can stay after 08/27 and application denied then how much she can stay after decision?
Please advise.

[newacct]

She can stay for an unlimited amount of time while the Extension of Stay application is pending.