Shimashita graduated from the Faculty of Letters and the Graduate School of Letters at Doshisha University.
She worked in corporate communications and branding for clients at a major advertising agency and in new-graduate recruitment and training at her own company. She later worked at a PR firm in Washington, D.C., providing branding-related support to Japanese companies entering the North American market. During this time, Shimashita became interested in the societal implementation of research done by academia and companies. After returning to Japan, she oversaw academic outreach work for the Graduate School of Science at Tokyo University and the National Institute of Technology (KOSEN). In 2021, Shimashita joined KII after doing public relations work for R&D startups.