Complex sentence: In 1922, she went to "Walkemühle", a progressive boarding school in Melsungen near Kassel, taking over from Nelson, who had founded it, until it was seized and closed by the Nazis in May 1933.
Split into simpler sentences: In 1922, she went to "Walkemühle", a progressive boarding school in Melsungen near Kassel, founded by Nelson. She then ran the school until it was seized and closed by the Nazis in May 1933.