She was her birth mother.
Li Liaoyuan was just in time when the show began. He has witnessed how the woman was trying to manipulate the things around with the help of her so-called niece around.
He may not know what she was planning but he was still the experienced one in the stream. One thing he has learned from his life was, 'It is better to keep your enemies in the front of your eyes, to know their tricks in better terms'. That would make you all prepared to counter their tricks before they hurt you fatally.
Seeing them leaving there would be no way he would be letting them leave. Even if he has to take the worst step to stop them, he would eagerly oblige. So interrupting the scene he had decided to reveal the truth.
"Rebecca, don't you feel regret in your life? Are you still planning to go away, abandoning you daughter behind", he asked in an accusing tone leaving everyone in a death shock.