They told the stories of extended relatives she never knew existed who died during the Holocaust.
Those letters have served as inspiration for the Vienna Project, a yearlong memorial to those killed during Nazi rule in Austria from 1938 to 1945. The project was conceptualized and is directed by Frostig, a resident scholar at the Brandeis Women's Studies Research Center.
"This isn't just another project for me, it has a family history that deepens what this means to me," she said.
The project, which started with an opening ceremony in October 2013, aims to fuse the arts, history, research, technology and activism.
It includes spray painted sidewalk stencils at 38 historic sites around Vienna, with a schedule of performance art, digital displays, readings and speakers at those sites.
One of the most important elements of the project, according to Frostig, is that it gives equal recognition to persecuted Austrian victim groups under Nazi rule, including homosexuals, the disabled, Roma and Jews, while preserving the historic record.
"This is a memorial that really rests in solidarity," she said.
It took some time to get Austrian government officials to warm to the project, but they have ultimately awarded it about €93,000 ($125,000) in funding, according to Frostig.
"At first people were very nice to me but I don't think they expected me to come back. They believed it was untenable: Too big and too complex," Frostig said. "I think they were distressed to see me come back, but gradually they came around and have agreed this is significant and they are standing by it."
Now, Frostig is working on putting together a collection of letters written by victims of Nazism in Austria that will be read during a closing ceremony at the Austrian National Library at Hofburg Palace.
Hundreds of organizations have been contacted in an effort to put the letter collection together, and individuals can upload their own family letters through the Vienna Project's website.
The closing ceremony is slated for October 18.
By Jarret Bencks // Reprinted with permission from Brandeis University