She subsequently led the negotiations on a coalition government with the Social Democratic Party (SPD).

From 1994 until 1996, she served – alongside Jürgen Trittin – as co-leader of the German Green Party.

From 2005 to 2009 she served as deputy chair of the parliamentary group of her party, this time under the leadership of co-chairs Renate Künast and Fritz Kuhn.

In addition to her committee assignments, she was a member of the Parliamentary Friendship Group for Relations with the Baltic States.

In 2016, Sager was appointed by Chancellor Angela Merkel to a three-member panel to oversee the implementation of a new law designed to avoid potential conflicts of interest, requiring senior German officials from the chancellor to deputy ministers to observe a cooling-off period if they want to quit the government for a job in business.