That mean she's not her daughter because the mother of Lin Jin Cheng exchange the female lead and her original son so she would thought that the female lead is her child. But still i'm happy that you found her son
@Nutsme i think they're twins and the old hag took the son to make him heir to the lin family, letting the mom think one of her babies was stillborn, because old-fashioned (read: stupid)people think that daughters are worthless except to marry off