Divorce immediately after GC thru husband

My sister is in divorce talks with her hubby over personal reasons. Her husband got his green card thru his employer recently, and she got hers along with him, as his spouse. They had filed their I-485 together.
Will she lose her green card status if he divorces her?
How long shouls the marriage last after getting the GC for her to hold on to her green card and related rights to work her in the US? Please advise soon.

If she does not have sufficient standing independently, that is she can't get an H1-B1, she may have to leave the country if he divorces her...