"You are a wonderful parent and you are doing everything in your power to make him/her better. Stay Strong and I am here whenever you need me!"
Something like that!
"What can I do to help?"
Be supportive. SOmetimes people need a break from the issue. Maybe you can take them away from the drama, at least for a little break.
First and foremost be sincere and supportive, if the person is your best friend you don't always have to say much other than do you feel like talking or ask for updates or the status also as a friend listen and try to do little things to smooth the bumps your friend is experiencing provide meals or practical assistance if possible but always remind your friend to never give up never never give up.
you are a wonderful parent and you are blessed everyday for being there for that child my son is a juenvile diabetic and im here for him also hes now 15 he was 7 when he was dignosed
Be positive and offer any to help them with anything they may need and to be there to listen and just hang out and be company for them if needed.
Keep the faith