Omer's parents divorced when she was a child, and when she was 11 years old, her mother was killed in a training accident, in the Hagana, a pre-state military organization. Her father, Moshe Mosenzon, was a newspaper editor who served in the Jewish Brigade. In his absence, Omer was raised by the kibbutz.

Omer began writing while she was a teacher, and continued with many books that reflect the developing state and culture of Israel. Most of her books are for young adults, and have been translated into many languages.

Omer received the 2006 Israel Prize for literature.