You will tell her that yo are sorry for her loss, and that you will always be by her side, in good and bad. You can tell her that life goes on and that she has to be strong, and to live her life. You can tell her that you will always help her, and that she has to try hard to go on and to enjoy in the rest of her life.
Be comforting and understand. Let her talk when she starts to open up. Talking about it helps it pass. Def let her know u are there good and bad and that it's ok to take time to heal but to remember there are still loved ones around to care for her.