I am so sorry to hear that. A good friend of mine just lost his two year old daughter to that. It's so hard to understand. I think the prognosis is supposed to be good if its diagnosed before the child is one and a half. I will pray for them. That's so sad.
I'm so sorry for your cousin. It's a situation I wouldn't wish on anyone. If she needs to talk to someone, please extend an invitation to me - we are 4 months into remission.
Kids (and babies) are really so resilient. They can take much more chemotherapy that adults can.