Jian Yiling's understanding of the Zhang family came from the second half of the original novel which she finished reading when she returned to her previous world.
In the second half of the novel, the Zhang family was a big help to Qin Chuan. They helped him accomplish many things.
After all, without the existence of the Lahaisen Hospital, the medical skills and expertise of the Zhang family were respected and acknowledged by everyone in the world. This meant that in the second half of the novel, they were able to help Qin Chuan save an important individual from a powerful family.
However, as Jian Yiling brought about several changes to this world, the original position of the Zhang family was replaced by Lahaisen Hospital.
