She studied (1961–63) English and American Literature at Aoyama Gakuin University, Tokyo, Japan.

From 1966 she attended Pratt Institute, Brooklyn, New York, as a fellowship student and earned her Master of Fine Arts in painting in 1969.

In 1996, Nii founded the non-profit Williamsburg Art & Historical Center (WAH Center) in Williamsburg, Brooklyn, New York, which is housed in the Kings County Savings Bank Building in the National Register of Historic Places - a New York City Landmark.

[6] Some of the artists include Ilya Bolotowsky, Jerry Rudquist, Ansei Uchima, Toshiko Uchima, Judy Chicago, Faith Ringgold, Toshiko Takaezu, Yoko Ono, Yayoi Kusama, Terrance Lindall, Doug Buebe, Beatrice Coron, Kenichi Nakajima, Charles Compo, and as well as her own artworks.

[1][8] In 2001, Governor George Pataki named Nii a "Woman of Excellence, Vision and Courage.