According to the Iskaheen RC Births, Charles McCann and Mary Barr had the following nine children:
1872 Aug 11 Mary McCann, Charles Barr, Mary McMacken, John Barr, Sarah Gortnamona, Muff
1874 Jul 3 Sarah McCann, Charles Barr, Mary McCallion, Hugh McCann, Bella Cruckglass
1876 Jul 30 Isabella McCann, Charles McCann, Mary McMackin, James McCallion, Isabella Gortnamona, Muff
1881 Jul 25 Anne McCann, Charles Barr, Mary McCallion, James McCallion, Nancy Gortnamona, Muff
1884 Jan 19 John McCann, Charles Barr, Mary Gallagher, James McCann, Bella Gortnamona, Muff
1886 Sep 4 Bridget McCann, Charles Barr, Mary McCallion, Michael McCallion, Sarah Gortnamona, Muff
1890 May 25 Elizabeth McCann, Charles Barr, Mary Gallagher, John McCallion, Sarah
1892 Jul 22 Thomas McCann, Charles Barr, Mary Gallagher, John Gallagher, Mary
1898 Jan 3 Andrew McCann, Charles Barr, Mary Bradley, William McCallion, Ellen
But there may be more not recorded at the Iskaheen RC church.
Oddly, enough Charles Petrucci's wife is variously listed as Anne Barr, Anne McCann and Anne Barr McCann..
Since Charles Petrucci and Anne McCann were married in 1913 in Philadelphia, I assume this is the same Anne McCann that I identified as a servant living there in 1910. So, it seems clear that Anne McCann wrote the postcard in question and finding out that she married Charles Petrucci completes the picture of what happened to her after that.
I assume that Andy McCann is the youngest child that Marie talked to in Gortnamona.