How should we make ethical decisions?

I don't know about you, but I took this class in healthcare ethics because I wanted to find out more about the dilemmas healthcare workers face everyday and how they come to terms with the inevitably difficult decisions they must make.
I am a pharmacist at Holmes Regional Medical Center in Melbourne, and I have worked there for 10 years now. Before that, I owned my own pharmacy and worked at a few different chain drugstores. As I have traveled through my healthcare experience, I have had occasion to discuss the seemingly heroic measures that many healthcare professionals provide in order to keep a patient alive. The question of whether to apply expensive therapies to patients who are determined to be "close to death" is an age old one and one I feel should be decided on by a case by case basis.
I had no idea until this week that there were helpful tools like the "Framework for Ethical Decision-Making" from the W. Maurice Young Centre for Applied Ethics. I guess I thought that there was some kind of decision-making guidelines out there, but now it is nice to finally see examples of them. Taking a difficult decision and breaking it down into the steps provided by this framework seems to help take the quess work out of whether your decision was "ethical" or not.
Recently, a 13 month old patient was admitted to our ICU because she was ventilator dependent since birth and electricity was cut to her home due to fire. She has multiple health issues including pulmonary hypertension which even an adult has difficulty surviving very long with. Our question in the pharmacy was "Is it ethical to keep this child alive due to her limited survivability and huge healthcare costs associated with her ventilator dependency?" Most of us felt that the child should be allowed to pass away peacefully due to the poor quality of life she (and her family) were experiencing.
I know there will be those that disagree wholeheartedly with my view. I am a mother and the idea that I would have to make this kind of decision is horrifying at best. The framework suggests that after you make your choice, you "Live with it" and "Learn from it". I only think that if this were indeed my decision to make that I would not only live with the knowledge that I did the right thing for the people involved but also learn that there is always pain associated with ethical decisions like this one.
I would love to hear your view if you have time to respond.
Lynne