For a number of years the school board of Allegheny published an annual report, and the one for 1875 gives some detail about schooling in those days, along with a little bit of information about Maria Ackley.
The schools had three basic levels of teaching - Primary, Medium and Grammar, and then some pupils might go on to High School elsewhere. This handbook details the curriculum for each level and also the salaries teachers earned. Women far outnumbered men in the profession, particularly at the more basic levels. If you had an appointment that took you up a level, your salary would increase. In addition, there was a sliding scale depending on your years of work experience. There was no confidentiality about salary, what you earned was published for the world to see.
So in May 1875 Maria was teaching at the Medium level in the 2nd Ward School. As such her salary for that one representative month was $55.
Perhaps others can tell us how well paid this was for the era in comparison with other trades and professions of the day.
For those who want to examine the book in detail for themselves, here is the link.
(With grateful thanks to Karen who provided the original reference)