My Wife's H4 Visa stamping is valid till 04/15/2013 per my old employer. Recently, I moved to a new employer via H1 Transfer and got my I-797/H1B approved till 06/06/2014 but haven't applied for her H4 extension. She is going to my home country for 3 months along with my US-born son and coming back on March 2012. Here are my questions:

1) Do I need to apply for her I-539 (H4 Extension) ? Or can she travel back to US via her old H4 Stamping by providing my new I-797/H1 Approval notice at the port-of-entry ?

Going by my current GC process, I will be able to apply my I-485/EAD by May 2012. So, just want to know if I am required to apply for I-539 (H4 extn) or not in my case.