In the beginning, when the Yun Family acquired Song Xiaoyu without any dowry, that naive girl couldn't get married legally due to her age. Eventually, she broke up with Yun Jianchen... leaving with nothing.
Song Yuan certainly wasn't as foolish as Song Xiaoyu.
Back then, Song Xiaoyu had stolen her fiancé. The fault clearly lay with Song Xiaoyu. Not getting married? Yun Zuoyi might not even have wanted to marry her!
But now the situation for Song Yuan is different. Her father, Song Guoji, is now the vice president of the Song Family conglomerate, a step away from the person in power. The Song Family's assets are not weaker than the Yun Family in any aspect. The third uncle is the vice president of the Song Family conglomerate, and the Yun Family needs to maintain a good relationship with the third uncle.
Besides, with Song Yuan carrying a child, even for the sake of the unborn baby... the Yun Family wouldn't mistreat Song Yuan.
