Contrast

It's not Song Yena who's fighting her. 

The one fighting her is the Curse caster ! That person has taken control of Yena's body through the curse, but their control is very shaky. 

From the time she saw the seven pagodas of the puppet on Yena's back, Claire knew such a day would come. As she looked at Yena's gleaming purple eyes and aura dancing around Song Yena, she realized the curse was meant to be the owner of Yena. hey… conversely, doesn't that mean they want to control commander Song of the base 

Seven pagoda's puppet mastery was not quite preferred among the dark arts practitioners. If practiced correctly, the puppet master would gain complete control over the body of the person. This is usually used for a very strong craftsman to use the slaves in a production line, or on death row prisoners to make them work. That is why it's not forbidden. It's used on prisoners mostly. In this manner, their brain is free, but their bodies are not.