Because she was decapitated in the accident, she couldn't remember her past. But another element is that no one claimed her body. So no one knew who she was, head or no head.
Her complete anonymity makes her different from the rest of the characters. Their childhood photos are displayed behind them as projections as each one is called into the spotlight. After Ocean concludes that even living 17 years is a gift, and the others agree, they decide that Jane Doe should be the one to go back into the world of the living, so she can experience life.