Queen and Grand Duchess
Sigismund Augustus informed his parents of the marriage on 2 February 1548 in Piotrków Trybunalski. The news caused an uproar among Polish nobles as Sigismund Augustus wed without the approval of the Senate. What was worse, Barbara was his subject and lover. Queen mother Bona Sforza was one of the most vocal opponents. In the ensuing campaign against recognizing the marriage, Barbara was widely accused of promiscuous behavior and of using witchcraft or poison to seduce Sigismund Augustus. Various authors, including Stanisław Orzechowski and Mikołaj Rej, published and distributed various derogatory pamphlets. The charge of promiscuity often enters works of modern historians though it is not based on any actual evidence. Lithuanian nobles did not openly protest the marriage, but were distrustful of the Radziwiłłs and their rise to power.
King Sigismund I the Old died on 1 April 1548. Sigismund Augustus, who briefly returned to Vilnius, had to travel back to Kraków to attend the funeral and secure himself on the Polish throne. Before he left, the King publicly announced his marriage and proclaimed his wife the Queen of Poland on 17 April 1548. By this act she also was legalized as the Grand Duchess of Lithuania.
During her husband's absence, Barbara stayed in Vilnius, in the royal castle. In May she informed him by letter that she is pregnant again; she either was mistaken or pregnancy ended in miscarriage, as the Queen briefly fell ill around this time. Since this is known only from Radziwiłł reports, it has also been proposed that the baby was another intrigue to influence the King. In September 1548, Sigismund Augustus invited Barbara to Poland to show the strength of their marriage. The issue was discussed by the general sejm on 31 October – 12 December in Piotrków Trybunalski. The sessions were loud and rowdy. The nobles, including voivodes Piotr Kmita Sobieński, Jan Gabriel Tęczyński, and Piotr Boratyński, pleaded the King to abandon the marriage and even threatened to take up arms. Sigismund Augustus steadfastly refused and stood by his wife; reportedly he even considered abdication. The sejm ended in a stalemate.
After the sejm, Sigismund and Barbara entered Kraków on 13 February 1549. In Wawel, Barbara enjoyed a luxurious lifestyle and expensive gifts. In May 1549, she received large territories in the Trakai Voivodeship, including Kaunas Castle, Rumšiškės, Alytus, Merkinė, Nemunaitis, Birštonas, Žiežmariai, Stakliškės, Karmėlava, Vilkija, Skirsnemunė, Veliuona, Darsūniškis. While she had immense influence on Sigismund Augustus, she showed no interest in politics unlike her ambitious cousin Mikołaj "the Black" Radziwiłł and brother Mikołaj "the Red" Radziwiłł. While they worked with her husband to secure her the Polish crown, she made no gestures to win support from the nobles or favor from the people. When a compromise solution was offered – recognize Barbara as Sigismund Augustus' wife but not to crown her as Queen of Poland – Sigismund Augustus refused because that would cast a doubt on legitimacy of any future children. In summer 1549, to protect himself from a possible armed rebellion, Sigismund Augustus concluded an alliance with Ferdinand, King of Hungary, leaving his sister Isabella Jagiellon to fend for herself in the succession disputes in the Kingdom of Hungary. He also worked to threaten, bribe, or otherwise persuade Polish nobles not to oppose the marriage. His mother and one of the most vocal opponents, dowager Queen Bona Sforza, left the court and moved to Mazovia.
During next sejm in May–July 1550, Polish nobility was not questioning anymore the validity of the royal marriage and Barbara was recognized as the King's legitimate wife. Therefore, while neither the sejm nor the senate gave an explicit permission, she was crowned as Queen of Poland on 7 December 1550 in Wawel Cathedral by Primate Mikołaj Dzierzgowski.
Dzierzgowski was an ally of Bona and was reluctant to recognize the new Queen. Sigismund managed to obtain recognition of his marriage by Vatican, and Pope Julius III in late 1550 called the Polish bishops to coronate Barbara. However, his order proved to be unnecessary, as the King had been able to make Dzierzgowski agree to crown his wife, before the envoy from Rome arrived to Poland. It was once thought that an edict prohibiting heresy, that would target protestants, issued by Sigsmund, was primary created to endear the Primate's favour for the royal pair. However, though winning over Dzierzgowski to Barbara's cause might have played some part, it appears the new law was mainly a result of civil disorder caused by some Protestant nobles.
Almost since her wedding in 1547, Barbara complained of poor health, particularly of abdominal pain or "internal stones". After the coronation her health took a turn for worse. She had fever, abdominal pain, lost appetite. A lump appeared on her stomach full of pus. Sigismund Augustus asked to send women healers, including a Jewish woman, from Lithuania.
In March 1551, her condition improved somewhat and she was able to receive a messenger from Bona Sforza who informed her that Bona recognized her marriage to Sigismund Augustus. It was described as Barbara's last victory. Her health continued to decline and she had fever, diarrhea, nausea. Sigismund Augustus personally tended to his sick wife even though reportedly she stank of pus. He wanted to take her to Niepołomice where he hoped that spring weather would lessen her suffering. When there was a doubt whether a special wagon to transport Barbara could fit through the city gates, Sigismund Augustus ordered the gate demolished. Barbara died on 8 May 1551 in Kraków. She asked to be buried in Vilnius and her body was transported to Vilnius Cathedral, where she was buried on 23 June next to Sigismund Augustus' first wife Elizabeth of Austria. Her death was a severe loss to the King; it is said that for a good portion of the journey he followed her coffin on foot. It was said that Sigismund Augustus became more serious, avoided parties, and liked to dress in black for the rest of his life.
The cause of her illness has been debated by contemporaries and historians. Secretary of Giovanni Francesco Commendone claimed that her illness was caused by her use of medications that were supposed to help to conceive a child. Radziwiłłs in their letters debated whether she had a sexually transmitted disease. There were persistent rumors that she was poisoned by Bona Sforza. Modern historians as the cause of Barbara's death point to cervical cancer or uterine inflammation.
