Does my spouse need H4 visa extension


My wife has H4 visa stamped based on my old employer and it will be expired on 31st Dec 2017. She has never traveled to US before. I had changed my employer and got the new stamping done. Can my wife apply for drop box directly before the old visa expires or do I need to apply for her #H4-extension based on my new employer? What could be the required documents for the eligible scenario