[2] Ishii received her bachelor's degree from Tokyo Women's Christian University in 1973 and her master's degree from Waseda University in 1975.

She studies arc spaces, a mathematical concept related to jets: arc spaces are varieties encapsulating information about curves on another variety.

[3] Ishii received the Saruhashi Prize for accomplishments by a Japanese woman researcher in the natural sciences in 1995.

[4] As a postdoc, Ishii was inspired by reading a profile of Fumiko Yonezawa, a physicist and former winner of the Saruhashi prize.

[3] Ishii received the Algebra Prize from the Mathematical Society of Japan in 2011.