Nan Cheng treated Dong Qianqiu as her 'daughter-in-law'? How did her inner monologue give the answer?

After Nan Cheng treated Dong Qianqiu as her 'daughter-in-law', her inner monologue was as follows: I couldn't help but feel surprised.  Dong Qianqiu's voice sounded like a girl's, and her eyes had a strange expression that made me feel puzzled. Did she really treat me as her son? But I quickly realized that there was no point in doubting. Dong Qianqiu is my biological grandson. How can I treat her as someone else? And since she's already my son, I should know her identity very well. I thought about it for a while and finally came up with an answer. Dong Qianqiu is my granddaughter, not my son. The reason why I treat her as my son is probably because I had some special experiences with her. I once spent an unforgettable time with her in Antarctica. At that time, we were trapped in the ice cave without food and water, and we had to rely on each other to survive. This experience is very precious to me, so I've always treated her like my own son. However, as I grew older, I gradually understood that some things were beyond our control.   Now that I finally knew Dong Qianqiu's identity, I finally understood my inner monologue. Although it's a little sad, I believe that this experience will make me stronger.