What mattered was not how good the movie was. The point was, because this movie was starring Hua Jin, and one of the investors was Huanyu. This meant that the show would definitely occupy the popularity rankings from the moment it was aired. Furthermore, Huanyu would do everything to promote it. That would only mean more exposure and popularity for the show.
What Li Jing lacked the most was popularity and audience. If she could use Hua Jin's current status to gain some popularity for herself, then needless to say, it was to her own advantage.
The role of the Kokakuchō didn't take up much of the show, but it was definitely an important character. Besides, it had a good persona and would certainly attract a lot of fans.