The quad was not hers. It was her father's.
Qiao Zijin was very clear of the concept of ownership. As such, she hinted to Ding Jiayi to sell the quad to pay for her treatment.
Ding Jiayi did not understand what Qiao Zijin meant by that, but Qiao Donglian did. It was exactly because he understood Qiao Zijin's intentions that he would never sell the house.
At this moment, Qiao Dongliang could never rest easy about Qiao Zijin. For her own benefits, Qiao Zijin was willing to sell the quad once and again. Without the quad, given Qiao Zijin's personality, there was no way she would care about the elderly couple, much less invite them to her large apartment to live with her.