Now, Cain's legacy may not be greater than Ryun's once she leaves high school. She needs to break the women's US 1500m record which is 3:57. If she breaks that next year, she will still be on pace to have a greater legacy than Ryun. If she medals in two days, that will also keep her on pace to have a greater legacy than Ryun, even if she doesn't break the 1500 record while in HS.
For Cain to officially solidify herself as the greatest young phenom in US T+F history, she needs to get gold in 2016. If she comes away with silver, there's still a chance that her legacy is greater than Ryun's.