Sibila was said to be a natural beauty in her early adulthood. She married her first husband, Artal de Foces on an unknown date. Upon her widowhood, Sibila became a lady in waiting to Peter's third queen, Eleanor of Sicily, during the royal couple's stay in Sibila's home of Empordà. Eleanor died in 1375; she had left Peter two surviving sons and one daughter.
Sibila attracted the attention of the king, soon after Eleanor's death. Sibila was in her twenties and Peter was fifty six. The king's sons, Martin of Aragon and John of Aragon soon found out what was happening. They were opposed the idea of their father marrying Sibila; the marriage could cause dynastic problems that could imperil their rights in the line of succession. Indeed, the announcement of the marriage of the lovers lead to some tense relations between the king and his sons.
On 11 October 1377, in Barcelona, Sibila married Peter IV of Aragon, thus becoming the fourth wife of the sovereign Aragon. She was the fourth wife of Peter, his previous wives were: Maria of Navarre, Eleanor of Portugal and Eleanor of Sicily. It is believed that before the marriage, Sibila gave birth to a son, Alfonso, who only lived for a year. The child's birth has been doubted and some do not believe in the child's existence, the only evidence of his existence is in the Chronicle of Peter IV of Aragon.
The couple had at most three children:
Alfonso of Aragon (1376–1377), Count of Morella, died young
Isabella of Aragon (1380–1424), married James II of Urgell and was mother of Isabella of Aragon, Countess of Urgell. Through Isabella, Peter and Sibila are ancestors to Joana, Princess of Portugal and John II of Portugal.
Pedro of Aragon (1378–1379), died young
Over time, things grew worse. Sibila's family were invited to court, the king became friends with Sibila's brother, Bernard. Peter, Sibila and her family made up one half of the court, the other half of the court was made up of Peter's son and heir, John, his infamous French wife Violante de Bar and their followers.
Peter died in 1387 and so John and Violant became King and Queen of Aragon. They wanted rid of Sibila. For her own safety, Sibila fled to Sant Martí Sarroca.