What does "four years in advance of the last fifty" mean?

The full text of the speech can be found at Women's History Guide.

A clue to the use of "the last fifty" can be found in a line that is read later on (emphasis mine):

Half a century ago women were at an infinite disadvantage in regard to their occupations. The idea that their sphere was at home, and only at home, was like a band of steel on society. But the spinning-wheel and the loom, which had given employment to women, had been superseded by machinery, and something else had to take their places.

This suggests two things. First, she was not referring to the last fifty years of the college, but to the last fifty years of advancement of women's equality.

Also, rather than being exact and writing fifty-six years, she wrote fifty years as an abbreviated way of referring to half a century, words which she actually used later on.

It's not precise, mathematically, but it seems she wasn't attempting to be precise.