Complex sentence: Beatrice was born in Coimbra around the period of 1347--1351 and she became Countess of Alburquerque when she married Sancho Alfonso, 1st Count of Alburquerque (1373).
Split into simpler sentences: Beatrice was born in Coimbra around the period of 1347--1351. Beatrice became Countess of Alburquerque when she married Sancho Alfonso, 1st Count of Alburquerque (1373).