I am so sorry for this terrible tragic loss you suffered. The pain and the grief must have been unbearable, only time can heal the grief and pain. Be comforted by her sisters words when you tried to blame yourself. Her sister knew how deep the depression went. You were not to blame.
She was in such a state of depression that she misjudged you and thought you didn't care. If she had been well as oz said she would probably have shrugged it off. So don't keep blaming yourself you were a victim of circumstances as so many on here are. I am so glad you came here and told us your story so we can share this with you. There is so much support here, so don't stop talking to us about how you are feeling.
All the best RosePetal