Like begets like

Cheng Yu wanted to give the duo privacy to talk so she excused herself and went to her room. 

Soon after Cheng Yu left, Madam Jiang thought of something and looked worried. "Luna, isn't it dangerous for you to be on your own? Xingyu told me that Li Xiyan escaped prison. She might seek you and cause trouble." Madam Jiang thought about Cheng Yu and was worried about her too. The last time, Li Xiyan had used her to force Luna into admitting guilt for a crime she had not committed. Since she was once again free, wouldn't she seek revenge on Cheng Yu as well? 

Since she was Luna's friend, she was concerned about her safety as well, and was even considering having both of them move in with her.