Illness and Photography

I've been home in Chicago the past week visiting my mother in the hospital who has been through a tough time suffering from a slipped disc and a stroke. I brought my camera with me to the hospital mostly out of both habit and instinct. When I was there and saw through my own eyes how fragile and close to the edge my mother was and how emotional me and my siblings were I did question whether I should make any photographs in this situation. I thought about it and it felt right for me - that the camera was for me a way of extending and documenting my emotional state. The next day when my other sister was in the hospital room and noticed that I had my camera she became angry with me as she considered that my mother would never want to see herself in that condition. This naturally caused some tension between my sister and myself and I was not inclined to fight for this given the support we were all there to give each other. For me though this does raise some serious questions. Did I have a right to photograph my sick mother when she was weakened and unaware of my camera? Was the experience that I was going through in the hospital those three days mine to capture however I choose? If I were a writer and wrote a story or in my journal about that experience would my sister have that same defensive reaction?