ДНК S03E89 - Выпуск 335. Русская американка!

American Laura wrote to someone else's sister and brother: "Hello, I'm your Sveta," and they grew up in an orphanage and can't believe that their sister lived in Pennsylvania for 25 years.
But if they have one mother, then why does the daughter of this woman categorically deny that the mother could have given up the child at all, not to mention three? So did Laura write to her blood relatives?