She left the company to go freelance citing a dispute over working conditions and abusive treatment by her editor.

Shinjo made her debut at publisher Shogakukan in 1994, drawing series for Shōjo Comic magazine.

[2] In 2007 she left the company, noting that her editors were excessively demanding and abusive, creating a stressful work environment.

[3][4][5] In her blog, Shinjo noted that though she was the actual creator of her manga titles, she was one of the last to know about any adaptation plans for her series, even learning about some through TV channel websites instead of her editor.

[6] When she decided to leave, one editor threatened to take all of her earlier series out of print, but Shinjo contacted a lawyer and the threat was never carried out.