How do I comfort a friend who recently lost a child?

A friend of mine lost her 4 year old son on June 26th to septic shock and organ failure after a long battle with cancer. I don’t really know how to comfort her. I don’t even know if it’s possible to feel comforted so soon after the loss of a child. I don’t have kids and I can’t even begin to imagine the pain that comes along with losing one. All I know is that she loved that child with all she had and she is absolutely crushed. I don’t know if “how do I comfort her?” is a valid question, because I’m not sure I could. But I want to be there for her. I just don’t want to say or do the wrong thing.