Mécia's life took an intriguing turn when she entered into her first marriage with Álvaro Pérez de Castro on September 29, 1234. Álvaro was a magnate involved in expanding the Castilian kingdom into the region of Cordoba. However, their consanguineous marriage stirred a dispute between Ferdinand III and Mécia's father and husband. The conflict was eventually resolved through the intervention of Queens Berengaria of Castile and Elisabeth of Hohenstaufen, Ferdinand's mother and wife, respectively.

While Mécia's first marriage remained childless, it thrust her into the heart of the struggles on the Cordoban frontier. As Álvaro oversaw the stronghold of Martos, the couple faced challenges caused by the conflict, including a localized famine. Mécia's resourcefulness and bravery came to the fore when she successfully defended Martos against an invasion by the Moorish ruler of Arjona.

Tragedy struck when Álvaro fell ill and passed away in Orgaz in 1239 or 1240. Mécia, now a widow, faced an uncertain future. However, she would soon find herself entwined in another royal union that would shape her life and legacy.

Mécia's second marriage was to King Sancho II of Portugal, son of Afonso II of Portugal and Queen Urraca of Castile. The legitimacy of their marriage has been a subject of debate among historians. While some have considered Mécia a mistress rather than a queen consort, the papal bull Sua nobis, issued by Pope Innocent IV, documents their marriage and is widely accepted as proof of their union. The precise date and location of their marriage remain uncertain.

Life at the Portuguese court proved challenging for Mécia. She faced political isolation and the disapproval of the Portuguese nobility and populace. Her foreign origins and previous marriage made her vulnerable to criticism and suspicion. The discontent within Portugal was not solely attributed to Mécia, as the country was already experiencing political instability. The king's decision to replace the royal court's counselors with his military companions led to conflicts and anarchy. Unfortunately, Mécia became an easy target for blame as her arrival coincided with the start of the Portuguese political crisis.

The marriage between Mécia and Sancho II faced opposition from the Portuguese clergy. They saw an opportunity to embarrass the king and hasten his downfall by challenging the union. The issue of consanguinity, as both Mécia and Sancho descended from Afonso I of Portugal, became a focus for the clergy. Pope Innocent IV, supported by the Portuguese bishops, issued a bull that decried the state of the kingdom and threatened "appropriate measures" if Sancho did not comply.

Sancho's refusal to repudiate Mécia led to his deposition and the subsequent kidnapping of the queen. Nobleman Raimundo Viegas de Portocarreiro, accompanied by men loyal to the Count of Boulogne (Sancho's brother and aspirant to the throne), seized Mécia from the royal palace in Coimbra and took her to the palace at Vila Nova de Ourém. Sancho, unable to rescue his wife, abdicated and fled to Toledo, where he eventually passed away in 1248. Intriguingly, Sancho's will did not mention Mécia, fueling speculation that he believed she was complicit in her own kidnapping.

Following her abduction, Mécia settled in Ourém. She made charitable donations and maintained good relations with the court's troops stationed there. While there are differing accounts of her subsequent movements, it is believed that she resided in the region of Castile, where she held lands. Tradition holds that Mécia passed away in 1270 in Palencia and was buried at the Benedictine convent of Santa Maria in Nájera, with her tomb adorned by the arms of Portugal.

Queen Mécia Lopes de Haro's life was marked by political turbulence and challenges. Despite the controversies surrounding her marriages and her perceived influence on Sancho II, she played a significant role in the Portuguese political crisis of 1245. Her resilience, resourcefulness, and determination to protect her territories demonstrated her strength as a noblewoman in a male-dominated era. Mécia's story serves as a reminder of the complexities and intrigues of medieval European royal courts and the indelible impact of strong-willed individuals like her on history.