So the actual prophecy was that someone who would resemble the original saint would bring prosperity to the empire. It doesn't say anything about the imperial family, which they didn't like, so they basically held her hostage and took her for themselves, saying that the prophecy was for her to be the empress.
The pope, in order to free her, lies and says that they got it wrong, and the chosen one is actually someone else and finds a replacement.
So technically, she never needed to be part of the imperial family to bring prosperity, the emperor was just a selfish coward. And what the pope lied about was when he told her that she wasn't the chosen one, because she is. By the end of everything, we can see she did actually bring prosperity, cleaning up the imperial family and helping the needy.
so what exactly changed in the prophecy? someone with pink hair is to be a crown princess but that someone needs to be way to young for the prince???