Diet acknowledging its status as a vassal of the Ottoman Empire. In September 1541, Isabella departed Buda and took up residence in Lippa, then in Gyál and Gyulafehérvár. She complained about ruinous state of her new domains and financial troubles. Isabella was young, noted for her beauty, and scolded for her expensive tastes. Three surviving pieces of jewelry are attributed to her: a diamond ring, a large pendant with 16 opals, and a gold necklace. She began reconstruction of the former bishop's palace in Alba Iulia in the Renaissance style according to the examples of Wawel Castle in her native Kraków and Royal Palace in Buda. She faced multiple political challenges: keeping peace with the Ottomans, containing Martinuzzi's ambitions, and blocking Ferdinand's attempts at taking over Transylvania. In December 1541, perhaps exhausted by her circumstances, Isabella signed an agreement with Archduke Ferdinand: she would abandon Transylvania and take up residence in the Szepes County. However, when Ottomans attacked again, Ferdinand did not have enough military power to defend his territories (see Siege of Esztergom (1543)) and the agreement remained forgotten. Poland proposed to solve the issue with another marriage – Isabella would marry widowed Charles V, Holy Roman Emperor, Archduke Ferdinand, or his eldest son Maximilian. But Ferdinand hoped that he could acquire Transylvania by other means. In 1548, when the Ottomans gathered all their forces for an assault against Persia in the ongoing Ottoman–Safavid War (1532–55), Ferdinand and Martinuzzi began negotiations to unite Hungary and defend it against the Ottomans. The agreement was reached on 1 August 1549 in Nyírbátor. Isabella would give up Transylvania in exchange for Opole and Racibórz in Silesia. Ferdinand was also to provide for John Sigismund, who would later marry one of his daughters. Martinuzzi was to be made Archbishop of Gran, and to receive the cardinal's hat. Isabella defended her rights and took up arms. She did not receive help from her brother Sigismund II Augustus as he concluded an alliance with Ferdinand so that he could quell opposition of Polish nobility to his marriage to Barbara Radziwiłł. Return to Poland In fall 1550, Isabella's troops defended Alba Iulia, but had to agree to a truce. She gained support from nobility in the diet of Aiud, but her forces were defeated near Cenad and she was besieged in Buda. In July 1551, facing superior forces, Isabella surrendered and signed the Treaty of Weissenburg.