H4 extension with H1b Amendment , is it possible ?

I have a situation here and I am in need of your suggestions on what best can be done in my case ?

I had a valid h1b visa + i-94 till 15 feb 2018 and my wife h4 was also valid till same date.

My employer filed H1b extension which was approved on april 18 2018 and it is valid till August 2020 but they forgot to file h4 extension for my wife. now my wife is currently out of status from last 2 months , now my employer is saying they will file an H1b amendment (premium processing) to add 1 more location and with it they will file h4 extension with nunc-pro-tunc. They are also saying if it doesn’t get approved she has to travel back to the home country and get a fresh H4 stamping.

My question is -

Is it possible to get an H4 extension approved , with H1B amendment ? How much percentage chance of success here ? OR what is the best course of action in this situation ?