Neilson would later credit Andrews with encouraging her to study history rather than English literature.

She rose to the rank of full professor in 1905, and stayed in that position until retiring from teaching in 1939.

Neilson graduated from Bryn Mawr – and later worked at Holyoke – with fellow medievalist Bertha Putnam.

Neilson's first major work was her doctoral dissertation, Economic Conditions on the Manors of Ramsey Abbey, in which she investigated the economic affairs of the lands held by Ramsey Abbey in the Middle Ages.

She edited three surveys of the lands owned by English monasteries, focusing particularly on the economic and social conditions surrounding them.