Ying Ying knew that her father actually didn't want to go --- at first, he just wanted her to save her sister so that he could die in peace. However, once he heard about Ying Ying's adventure to search for the man, he looked up at her in surprise. Of course, Ying Ying didn't tell her about how she sold her body because it would only make her father feel disappointed but she didn't bother to cover up that she had given her loyalty to Yao Ling.
Besides, in their current position, it would be hard to regain their previous glories and Ying Ying's father couldn't refute that. He could only sigh in sadness, knowing that this happened because of his loyalty to someone that maybe had been dead...
However, he got a hint of hope when he heard Ying Ying's story about that man. Even though Ying Ying admitted that she had never directly met the man, hope was still hope --- it was better than nothing.