Why was Rachel forced to give her daughter up for adoption in the novel, Daughter of Moloka'i?

Rachel, Ruth’s birth mother, was forced to give her daughter up by the government because she and Ruth’s dad were confined to a leper colony. She lives long enough for science to find a cure, and she is eventually able to leave the colony. She lives in Hawai’i but contacts Ruth one day. When Ruth realizes why she was given up for adoption, she agrees to meet her mother, and the two develop a close relationship. Rachel also develops a close relationship with Etsuko who is not threatened by the new mother figure in Ruth’s life.