I agree with Peg...
there is nothing at all that can be said. to be honest i dont think that there is any right words... just alot of wrong ones iykwim
I would send a thinking of you card and just keep it simple just let them know that you are thinking of them and that if there is anything you can do to help them please let you know.

You sound like a wonderful friend to be thinking of them. If you need any help PM me and i will see what i can do!!