H4 interview when H1 extension is approved but not stamped

[jayaprataab]

My H1 is expiring by April 7th and I applied for H1 extension and got approved but not yet stamped...
Can my wife now appear for Interview for fresh H4??..if she appears,what is the expiry date will she get, will it be my old i94 expiry date(April 7th) or my new H1 approved petition date???

Thank you...