First of all, due to the death of Zhou Ziran, the acting queen, and his son, and Dou Yifang's identity as a spy in Xueyuan, he has a heart for Dou Yifang. Moreover, Er Shen also said that Xueyuan didn't marry him because Dou Yi wanted to keep Xueyuan around, threatening him and containing him. So, Er Shen wanted to help him, let him lead troops to fight, and at the same time let him force the palace in the name of Jun Qing, and force the emperor to abolish it. Then, Er Shen found Xueyuan again, threatening Xueyuan with Zhou Yafu's life (because Zhou Yafu will die in the end as long as he is forced to live, while Er Shen can keep him from being forced to live), so that she can frame Dou E and say that she is not perfect. In fact, this is not enough to kill Dou E's injustice, but it will plant a knot and doubt in the emperor's heart, making it very convenient for her to frame the plan behind it. Xueyuan loves Zhou Yafu and Dou E's room. She is in a dilemma, so she promises Er Shen for a pretence. She wanted to tell the Queen to forgive Zhou Yafu and save her life. However, after she tentatively asked, the queen's words and her own understanding of the court struggle made her feel hopeless. So, she was in a dilemma and committed suicide to save swallowing gold. After the death of Xueyuan, Dou Yi remembered Xueyuan's kindness and asked Dou Changjun to help find out Er Shen's conspiracy. She decided to avenge the death of Xueyuan. First of all, it's Er Shen's fault, and second, it's Zhou Yafu's stupidity. Therefore, she used the life of Er Shen's child to force Er Shen to admit all the crimes. Er Shen died after a glass of poisoned wine. Zhou Yafu forced other c to revolt and wanted to unite with Zhou Yafu. Dou used Zhou Yafu's loyalty to the Queen Mother to lure Zhou Yafu into the palace and capture him alive, that's all.

In fact, I think the snow kite can not die. She just needs to make things clear to the queen. I believe that with Dou's wisdom and personality, Zhou Yafu can be saved. She committed suicide mainly because she was full of despair about the court fight.