When is it time to let a terminally ill child go?

A friend of mine asked me this question and wanted to know my opinion. I’m kind of stuck. Her almost 5 year old son is currently in the ICU with septic shock. He was born with a hereditary form of kidney cancer and has had AML leukemia and a rare liver tumor. He was finishing up his latest round of chemotherapy, a new regimen, and developed a nasty infection. He is in a lot of pain, organs are failing due to the septic shock and he is very very ill. I know what I would do in her situation. But I don’t know her all that well, I met her at a cancer conference not too long ago. She has asked my opinion on many things, and while I have no problem offering her support and someone to talk to, I don’t want to influence her in her choice to keep her son alive or not. I’m not sure what to tell her. Any suggestions?