Apply for H4 Extension when H1 Extension is pending

[hvarada]

Hello Experts,

I'm currently working on my H1-B Visa and have a stamped Visa till Aug-15 2018. My wife as well have a stamped H4 Visa till the same date.
My wife had to travel India at my petition time, due to which; only my H1-B Visa extension petition was filed with USCIS (2 weeks ago) and its under pending stage right now.
My wife is back to USA; In this case;
1. Can I apply for my wife's H4 extension based on my H1-B receipt number right today (while my visa is still under processing stage)? (OR)
2. Should I have to wait till my H1 visa is completely approved and then file for her H4?

Please advise.!

Thanks!