Princess Eleonore Erdmuthe of Saxe-Eisenach

In Leipzig on 17 April 1692, Eleonore married secondly John George IV, Elector of Saxony[4][5] and moved with her children to Dresden, where the Saxon court was established. The wedding was concluded at the insistence of Frederick III, Elector of Brandenburg (who wanted to secure an alliance with Saxony)[lower-alpha 1][6] and the Dowager Electress Anna Sophie of Denmark, ostensibly to produce legitimate heirs to the Electorate of Saxony but truly to end the liaison between her son and his mistress, Magdalene Sibylle "Billa" of Neidschutz.

The union proved to be unsuccessful;[2] John George IV lived openly with Billa, and she became the first ever Official Mistress (Favoritin) of an Elector of Saxony; while Eleonore was relegated to the Hofe (the official residence of the Elector).[1] In addition, the Electress suffered two miscarriages during their marriage, in August 1692[4] and February 1693,[7] and a phantom pregnancy in December 1693.[8] In March 1693 began rumors at the Saxon court that Eleonore was not the lawful wife of John George IV, because at the time of their marriage, he was already married with Billa;[9] There was even found a document confirming the conclusion of a marriage contract between the Elector of Saxony and his mistress, but John George IV (probably fearing the anger of the Hohenzollerns) said that he did not consider this contract as a formal marriage, and that it was only made for the purpose of legitimizing his offspring with Billa.[7] Nevertheless, throughout his marriage, John George IV desperately wanted to legitimize the relationship with his mistress and tried to get rid of his wife and her children; fearing for her and her children's lives, Eleonore left the Hofe and settled in Pretzsch.[10] During this time, Eleonore confided in the English diplomat George Stepney, who wrote extensively about her and the Saxon court.

John George IV died on 27 April 1694 from smallpox after being infected by the dying Billa.[10][11] The new Elector, Frederick Augustus I allowed the Dowager Electress and her children to remain in Pretzsch, where they lived until Eleonore's death two years later, on 9 September 1696.[10][11][12] She was buried at Freiberg Cathedral.

After her death, Eleonore's children were sent back to Ansbach to the court of their older half-brother George Frederick II,[5] who became in the new Margrave of Brandenburg-Ansbach after Christian Albert's death in 1692. George Frederick II, as well as his predecessor, was a minor and ruled under a regency, who had little interest in the education of the children. William Frederick stayed in Ansbach and in 1703 after the death of his brother inherited the Margraviate; Caroline went to Berlin at Charlottenburg Palace under the care of Frederick III, Elector of Brandenburg, and his wife, Sophia Charlotte of Hanover, who was a friend of Eleonore.[2][10][13]