House of Lara
Mécia was married on 29 September 1234 to Álvaro Pérez de Castro, a magnate involved in the expansion of the Castilian kingdom into the region of Cordoba, whose first marriage to Aurembiaix, Countess of Urgell had been annulled in 1228, while Mécia's sister Teresa married Nuño, Count of Rousillon, a kinsman of the powerful House of Lara.