H4 extension required?

Myself and my wife had stamped visa until August 21st 2021 based on the approved H1b petition. I travelled to US and transfer to a different employer. The updated i94 i got is Jan 2021. My wife travelled to USA on August 2020 and she got i94 until Sep 2021. Her stamped date in PP is until August 2021.
Now my employer has filed extension for me. Being the dates are still valid for my wife I could apply for H4 extension anytime before 6 months of expiry right? Please clarify if I am right or wrong.