How did Qingling become the king of the daughter country?

According to the plot of the TV series "new journey to the west", before being reborn, Qingling was a green snake, cultivated into human form under the protection of the old king. After the death of the old king, Qingling was crushed by the Buddha at the foot of Wuzhishan in order to save the Monkey King. Qingling didn't give up, so she gathered three souls and seven spirits and attached herself to the old king's body, thus realizing reincarnation and becoming the king of the daughter country.