Catherine Collins is the late wife of Jamison Collins, mother of Elizabeth Collins, and Roger Collins, Grandmother of Carolyn Stoddard, and David Collins, and daughter-in-law of Edward Collins, and Laura Murdoch.
It was originally outlined by Art Wallace in the series bible Shadows on the Wall that Elizabeth's father was named Joseph and her mother was named Carolyn. As told by Wallace, Carolyn had died at age thirty-eight as the result of giving birth to Roger.
This character appears in the 2012 audio A Collinwood Christmas.
In episode 354, Roger mentions an "Aunt Catherine" to Carolyn, but she's never mentioned again in the series, and it's unclear which side of the family she's on. The Catherine of A Collinwood Christmas is Roger and Liz's mother, so she couldn't be the "Aunt Catherine" that Roger is referring to.