From Lin mouth, Sara learned about Caroline's appearance many years ago.
Twenty years ago, both of them were unmarried female and the same peerless genius. Heroes cherish heroes, and geniuses naturally cherish geniuses. They were so well-matched that they became best friends.
The Lin family very hated traditional American medicine, and did not allow Lin and Caroline to communicate. At that time, Lin was, after all, a little girl, not the island owner's wife who was so powerful that she dared not disobey the orders of her family, so she could only secretly contact with Caroline. This friendship was only known to a few people.
When the two were seventeen years old, Caroline and Lin were with a famous professor at that time to do research. At this time, Caroline knew the man who was likely to be Sara's biological father.