Birthler was elected to the only democratically elected People's Chamber in the GDR in March 1990, where she served as spokeswoman of the Alliance 90. From German Reunification on 3 October 1990 until the elections of 2 December 1990, she was a member of the Bundestag, the Parliament of Germany. In October 1990, she became a member of the state parliament of Brandenburg, and in November, she was appointed as Minister for Education in the state government of Minister-President Manfred Stolpe.