Women in mystery fiction were largely confined to little old lady snoops - amateur sleuths - who are nurses, teachers, whatever.
The 1890s was a decade when life began to change in urban America. Modern conveniences that we now take for granted came into use; women's roles became less restrictive; and San Francisco, a port city with influences from all over the world, was a lively place in which to reside.
Anna Katherine Green wrote about a female inquiry agent, and there were a scattering of female investigators in the 1970s, authored by men, who just didn't ring true. So I thought, 'Well, there's an opening here for something.'