Born 1894, Buffalo, New York, United States, died 1961.
Worked in Wilfrid Voynich's bookshop and was a long-term companion of Ethel Lilian Voynich, who left her the Voynich Manuscript. Nill eventually sold the document to Hans P Kraus
Two photographs of her can be found here  (along with those of others connected with the VM): other traces can be found on the Ellis Island website and Google Images etc.
More information can be found here and here, and in other websites on the Voynichs and the manuscript.
Details of her will here.