Dulce's bethrothal to infante Sancho, son of Afonso Henriques, the first king of Portugal, was celebrated when she was eleven years old and the marriage in 1174.

[6] "A beautiful and excellent lady, quiet and modest, her personality coinciding with her name,"[c] Dulce was used as a commodity to seal an alliance which aimed to "strengthen Portugal and to contain the expansionism of Castile and León" and she played the role that was expected of her as a wife and as the mother of numerous children.

[2][7] At the same time, the marriage compensated for the broken engagement of her husband's sister, Infanta Mafalda with her brother, the future King Alfonso II of Aragon.

In his first will, executed in 1188, her husband gave her the income from Alenquer, of the lands along the banks of the Vouga River, of Santa Maria da Feira and of Oporto.

[6] Dulce did not live long after the birth of her last two daughters, Branca and Berengaria, probably twins, and died in 1198 probably succumbing to the plague and weakened by the successive childbirths.