Sigrid Kopfermann (June 30, 1923-June 25, 2011) was a German painter, graphic artist, and art teacher.
Biography on German Wikipedia: From Google Translate

Landschaft (Landscape) by Sigrid Kopfermann
1993 / Mixed media on canvas / 39-2/5″x27-2/5″ / Found on Van Ham auction site

Sigrid Kopfermann on Artnet: http://www.artnet.com/artists/sigrid-kopfermann/

Further reading:
https://www-kopfermann–fuhrmann-de.translate.goog/sigrid-kopfermann?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc
https://ocula.com/artists/sigrid-kopfermann/
https://www-galerie–swetec-de.translate.goog/sigrid-kopfermann.htm?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp