Sonia grew up in the Keep of Weld. Her mother died when she was little, and her father despised her, due to the belief that only a male could become Warden of Weld. Her only friend in the Keep was Annocki, her maid, who cared deeply about her. Sonia resented and felt bitterness towards her father because of his indifference towards her and the fact that he would not make her the next Warden of Weld because she was a girl.
When the Warden offered the Title of Warden to the young man who managed to find the source of the skimmers and destroy them, Sonia saw her chance to prove herself and claim the title. She switched places with Annocki so that no one would suspect she was gone, and tried to get a competitor to let her go with him through one of the Three Doors. Sonia did not have any luck until Rye of Weld arrived. Despite his protests, she managed to go through the Golden Door with him and arrived centuries into Dorne's past, although neither Sonia or Rye knew that at the time.
The two companions travelled through the forest where Rye was entrusted with some magical charms. If it were not for Sonia, they would never have made it out of the forest alive. Sonia was also one of the signs the Fellan we're searching for to identify the right person to give the charms to, as she was a magic-wielder, and half-Fellan. In the town of Fleet, Sonia met Faene of D'Or, and found out about the truth of the Gifting. When Olt's soldiers came to collect Faene, Sonia and Faene hid in a secret compartment in Faene's parents' grave. However, they were discovered, and taken to Oltan to be sacrifices in the Gifting. In Oltan, Sonia struggled against her captors and was eventually put to sleep to silence her. To help Rye find her, she left a trail behind her of stones she had found in the forest. During the Gifting, Sonia remained calm and helped Rye rescue herself, Faene, Dirk and the rebels and the other prisoners. After Olt's death, she travelled with Faene, Dirk and Rye back to Weld, where she left Faene in the care of Annocki. Then she, Rye and Dirk went through the silver door.
Sonia is slight for her age, slim but strong, with curly red-copper hair and brilliant muddy brown eyes with a tinge of green. Her bright hair is described in a passage as seeming to "light up the room" and her eyes were seen as fierce. Her hair and eye colour mark her out as one with Fellan blood.