Why didn't Yang Guo keep Xiangyang?

At this time, the battle of Xiangyang started, but because Guo Jing and others have been worried about the preparations for the Mongolian army's comeback for eight years, Xiangyang City was impregnable and beat back the Mongolian army's attacks again and again. Although Yang Guo wanted to help Guo Jing defend the city, he didn't want the little dragon girl who was seriously ill to suffer. He saw Guo Jing guarding the city well and thought that the Mongols could not attack Xiangyang for many years. Soon after, he left with the little dragon girl. Little dragon girl's illness should come from her old age delivery. Since the woman in yellow is the descendant of the condor heroes, the little dragon girl must have a son. Little Dragon Girl is four years older than Yang Guo. She was thirty-eight when she retired, which means she was at least forty when she gave birth. Although she is successful in internal work, she can't resist the aging of her body. In addition, she suffered from the affair poison and the internal injuries that were interrupted when practicing the Jade Girl Heart Sutra. A storm of giving birth to a child at an advanced age made her almost die in childbirth. Fortunately, she was born, but this led to complications and serious illness.