Leonor Castro de Mello y Meneses (born 1512, died March 27 of 1546, in Gandía) was the IVth Duchess of Gandia.
 She was a noble Portuguese and the Lady and close friend of the Empress Isabella of Portugal.
 She was daughter of Álvaro de Castro "the Old", Captain-general of Africa of King Manuel I of Portugal, and of Isabel de Melo Barreto e Meneses.
 Her brother, Rodrigo de Castro, was governor of the Portuguese seat of Safí (Morocco).
Isabella of Portugal (Portuguese, Spanish: "Isabel"; French, Dutch, German: "Isabelle"; English: "Elizabeth"; 24 October 1503 – 1 May 1539) was a Holy Roman Empress and Queen of Spain, Germany, Italy, Naples and Sicily and Duchess of Burgundy by marriage to Holy Roman Emperor Charles V, and regent of Spain during the absence of her spouse during 1529-1532, 1535-1536 and 1538-1539.
Maria Josepha of Bavaria (Marie Josephe Antonie Walburga Felicitas Regula, 20 March 173928 May 1767) was Holy Roman Empress, Queen of the Romans, Archduchess of Austria, Grand Duchess of Tuscany, etc. by her marriage to Joseph II, Holy Roman Emperor.
 By birth, she was a Princess and Duchess of Bavaria as the daughter of Charles VII, Holy Roman Emperor, Elector of Bavaria, and Archduchess Maria Amalia of Austria.
Beatrice of Burgundy (1143 – 15 November 1184) was a Sovereign Countess of Burgundy from 1148 until her death, and a Holy Roman Empress by marriage to Frederick I, Holy Roman Emperor.
 She was crowned Holy Roman Empress by Antipope Paschal III in Rome on 1 August 1167, and as Queen of Burgundy at Vienne in August 1178.
Tello Pérez de Meneses (died c. 1200) was a Castilian magnate and military leader under the reign of King Alfonso VIII of Castile, and the ancestor of the Téllez de Meneses, a prominent noble lineage, whose descendants include several royal members such as Queen María de Molina, Tello's great-granddaughter, and Leonor Telles de Meneses, queen consort of Portugal.
 Tello participated in several military campaigns during the Reconquista and subsequent "Repoblación", and was also a generous founder and patron of monasteries and hospitals for captives and lepers.
 Together with the Girón, the Téllez de Meneses were among the most influential and powerful aristocratic groups in Tierra de Campos.
Maria Theresa of Naples and Sicily (6 June 1772 – 13 April 1807) was the last Holy Roman Empress and the first Empress of Austria by marriage to Francis II, Holy Roman Emperor.
 She was the eldest daughter of Ferdinand IV & III of Naples and Sicily (later Ferdinand I of the Two Sicilies) (1751–1825) and his wife, Marie Caroline of Austria (1752–1814).
D. João de Castro (7 February 1500 – 6 June 1548) was a Portuguese nobleman and fourth viceroy of Portuguese India.
 He was called "Castro Forte" ("Stronghold" or "Strong Castle") by poet Luís de Camões.
 Castro was the son of Álvaro de Castro, civil governor of Lisbon.
 His wife was Leonor de Coutinho.
Holy Roman Empress or Empress of the Holy Roman Empire is the title given to the consort (wife) or regent of the Holy Roman Emperor.
 The elective dignity of Holy Roman Emperor was restricted to males only, therefore there was never a Holy Roman Empress regnant, though women such as Theophanu or Maria Theresa of Austria, who controlled the power of rule, served as de facto Empresses regnant.
Constance (2 November 1154 – 27 November 1198) was Queen regnant of Sicily in 1194–98, jointly with her spouse from 1194 to 1197, and with her infant son Frederick II, Holy Roman Emperor, in 1198, as the heiress of the Norman kings of Sicily.
 She was also Holy Roman Empress by marriage to Henry VI, Holy Roman Emperor.
Adelaide of Italy (93116 December 999), also called Adelaide of Burgundy, was a Holy Roman Empress by marriage to Holy Roman Emperor Otto the Great; she was crowned as the Holy Roman Empress with him by Pope John XII in Rome on February 2, 962.
 She was regent of the Holy Roman Empire as the guardian of her grandson in 991-995.

Question: Who was this Holy Roman Empress and Queen of Spain, Germany, Italy, Naples and Sicily and Duchess of Burgundy whose influential friends include Leonor de Castro Mello y Meneses?
Answer: Isabella of Portugal