As all the respondents above said, Christine did it on purpose. She was also very conflicted before she did this. You can see that Christine was in the secret room before this. Very painful. Because to him she deeply admired this angel of music. You can also see a lot of police officers with guns in the play Don Juan. They had expected that the Phantom would appear during the performance of Don Juan, and only Christine had seen the Phantom, so they asked Christine to help expose the Phantom so that those people could catch him.

What I want to say is that although Christine loves Raoul, although she helped uncover the Phantom's mask. But she really liked and admired this musical angel, and she always thought that he was sent by his father to help and accompany her. And she was deeply attracted by Phantom's talent. You can experience this in subsequent episodes.