Kahlo died at age 47 in 1954. The following year, her widower, the muralist Diego Rivera, gave the painting to a woman who had helped Kahlo in the studio, Stein said.
The recipient took the work home to California. Now in her mid-90s, she offered it to Sotheby’s this summer, he said.
The auction house declined to comment on why the owner sought to sell the piece.
“Niña con Collar” is among the first 20 of Kahlo’s 143 paintings, Stein said. It prefigures hallmarks of the artist’s self-portraits, including winged eyebrows and the full frontal gaze.
The subject, a girl of about 13 or 14, stares directly at the viewer. “There is a sense of warmth and closeness,” Stein said.
As in some Kahlo self-portraits, there is little depth. The background is a mix of indigo and sky-blue; the face of the girl is copper-brown. She wears a jade necklace that appears in other paintings by the artist.
In international art markets, works by Kahlo have fetched more than any other Latin American artist, said Stein.
Frida Kahlo painting, unseen for 60 years, surfaces for sale | Reuters