Sonia Gechtoff (September 25, 1926-February 1, 2018) was an American abstract expressionist artist; her primary medium was painting.
Biography on Wikipedia: https://en.wikipedia.org/wiki/Sonia_Gechtoff

Etya by Sonia Gechtoff
1958 / Oil on canvas / 109″x68″ / Oakland Museum of California

Sonia Gechtoff on Artnet: http://www.artnet.com/artists/sonia-gechtoff/

Further reading:
https://www.annexgalleries.com/artists/biography/783/Gechtoff/Sonia
https://hyperallergic.com/521757/a-forgotten-painter-and-her-visionary-abstraction/
https://news.artnet.com/art-world/sonia-gechtoff-obituary-1217393