The commercial databases appear to have little on Mary Isaak. JSTOR gets zero hits for the search (full text of a VERY large set of scholarly journals) "mary isaak". It might be worth reading the 3 articles found by the search: "abe isaak" to find some indirect mention of Mary. But the zero hits for the "proximity searches" "abe mary isaak"~25 and even "abe mary isaak"~50 are not encouraging - and even the VERY broad search: "abe isaak" AND mary still gets zero hits. The one hit for: "abe isaak wife"~20; "Anarchism and the Assassination of McKinley". Sidney Fine. The American Historical Review, Vol. 60, No. 4 (Jul., 1955), pp. 777-799 says (p.781) "On the night of the assassination Chicago police arrested Abe Isaak, Sr., his wife, his son, and his daughter, and five other Chicago anarchists...", and (p.782) "the women, of whom there were three, were first allowed to bail and then later in the day released(21). Note 21 is: Chicago Tribune, Sept. 7, 8, 9, 1O, 19O1; Free Society, Oct. 6, 19O1.
Possibly a painstaking Interlibrary Loan for these papers would give you more, but ILL is notoriously disappointing on many older newspapers. I would recommend a thorough search of Worldcat to find libraries that still own these papers. This means following the Worldcat hot links to the individual libraries' catalogs, to see if in fact they DO still own the needed years of the newspapers. I would be tempted to find a sympathetic reference librarian at the libraries, to check the references. But JSTOR covers quite scholarly journals - and it's certainly not unreasonable to trust those references, especially if you are on a deadline. Worldcat.org Advanced search for author: isaak, mary seems to get only a much different Mary Isaak. If you are near an academic or VERY large public library that has access, I would recommend the commercial Worldcat, that gets 58 hits for the search: mary isaak - though the 51 for the same search in worldcat.org basic (default) search may be just about as useful.
Google's Web search for "mary isaak" "abe isaak" might give leads among its links to uncataloged collections and other sites. The search: "mary isaak" "abe isaak" site:edu (4 hits) seems too restrictive.