Here's why:
* Rebecca's Secret: Rebecca is Sutton's biological mother, but she gave her up for adoption as a baby. Sutton was raised by adoptive parents.
* The Twist: The story focuses on the mystery of Sutton's birth mother and the connection to the twin sister she never knew she had, Emma.
* Revealing the Truth: Throughout the series, there are clues and hints that suggest Rebecca's connection to Sutton, but the truth is not explicitly revealed until later in the storyline.
It's a major plot point in the show for Sutton to discover the truth about her biological mother and the role she played in their lives.