Can we file h1b extension plus h4 COS + EAD for same applicant?

My wife is currently on h1b status (6th year) which is about to expire on Jan 6th. Her I-140 is approved just now. Is it possible to file her H4 Change of status (COS) + EAD in December and then apply for h1b extension (not premium) in January before Jan 6th?

h1b extension (not premium) will take around 6 months to approve
H4 COS + EAD is likely going to take 6 to 8 months

Can she continue to work on h1b extension receipt while waiting for h1b approval and also on the side H4 COS + EAD will be processing?

She’s good if H1b extension gets approved and she’s also good if H4 COS + EAD gets approved together. However if h4 gets approved first and EAD gets approved there will be gap in employment?