I won't write the switch, I'll just show it to you.

First, thirteen years later, the girl was bought back to Shuifu to be an inferior handmaid, and then abused by all parties. But there must be good people, and because these good people know the history of this family, they think about their own life experiences and wonder if they are the girl. Then something incredible happened. Whether she is really Shuifu's daughter or not, events are developing in this direction, including conspiracy and danger. Finally, it can be explained that her motivation is to "get back everything she lost", including feelings.

As for the ending, it depends on what you think.