In October 1796.
Caroline von Wolzogen's novel Agnes von Lilien begins anonymous serialization in the monthly Die Horen, edited by her brother-in-law Friedrich Schiller.
It is considered an important work of German Romanticism and was one of the earliest German novels written by a woman.
https://en.wikipedia.org/wiki/Caroline_von_Wolzogen
Wolzogen's works in the German writer's Sophie database:
https://scholarsarchive.byu.edu/do/search/?q=author_lname%3A%22Wolzogen%22%20author_fname%3A%22Caroline%20von%22&start=0&context=5485626&facet=