The ceramic bust is of French painter and sculptor Jean Dubuffet's grandmother from Mrs Grehan's French period, 1970-83.
It is also from a private collection, but there are several more from that period for sale.
Works from"Dance" in her "Movement", and "Landscape" series will be offered, as will Mrs Grehan's "Trees" series from her 1975-83 period, and works from the New Zealand Trees series when she returned home to live.
Exhibition curator Bill Milbank said the works were the remainder of Mrs Grehan's work from her studio, apart from a small number currently showing at the Sarjeant Gallery. Most of the works are for sale and will fund a publication Mr Milbank is compiling of Mrs Grehan and her works. The book about her life is in draft form and close to the print stage.
The draft will be available for viewing at a morning tea at the Sarjeant Gallery on Wednesday next week, where her only son, Oxford University Professor Martin Oldfield, will speak.
Wanganui born, Mrs Grehan, nee Brodie, attended Wanganui Girls' College then completed a fine arts degree at the Canterbury College of Arts in Christchurch (Ilam School of Fine Arts) and then the Camberwell School of Art in London.
In 1983 Mrs Grehan returned to New Zealand and lived in the Bay of Islands with her husband.
Following his death, she returned "home" to Wanganui in 1996.
Mr Milbank said Mrs Grehan's "great enthusiasm and diverse artistic skills greatly enriched the Wanganui cultural fabric up until her sudden death".
"She was a very interesting New Zealand artist."
Of her remarkable diverse creative output, Mr Milbank said Mrs Grehan was well established and her work sold well in France.
The two exhibitions (at the Milbank and Sarjeant) are a good, strong statement of her achievements, he said.