Who was rosemary and what what happened to her?

Rosemary was the Giver's daughter. He loved her and trained her with happy memories, but once he gave her the memory of a child taken away from its parents, she changed (she now knew pain.) She insisted that the Giver not spare her the painful memories she knew would soon come. One day after an especially hard session, she applied for release. With bravery the Giver had never felt, she chose to inject herself.

When she died the memories she acquired transferred to the people of the community. The citizens had not before experienced such pain, and there was largely chaos within the community. The name Rosemary was forbidden, and most get uncomfortable when the topic is mentioned.