The most important thing you can do is assure her that God is even more concerned about what she's gone through than she is. God loves her, and He not only knows what has happened to her, but He also wants to help her get through it.
Almost nothing can be as devastating as the end of a marriage. It can be as heartbreaking as the death of a loved one, because (at least in most cases) it's so final, and leaves an empty place in the lives of those left behind. Not all divorces end this way, I know -- but the pain and the shattered dreams often remain long after the divorce has taken place.
This is one reason why divorce was not part of God's original plan for the human race. He knows the hurt and the grief it causes, and because He loves us He doesn't want us to have to go through this. "'I hate divorce,' says the Lord God of Israel.... So guard yourself in your spirit, and do not break faith" (Malachi 2:16).
Ask God to help you understand the pain and confusion (and even guilt) your colleague is going through. Then ask God to give you opportunities to let her know you care. Don't try to dig up the past (unless she wants to share it with you). Focus instead on the future, and urge her to turn to Christ. In addition, many churches have special divorce recovery programs to help people face the future with hope.