From census data it looks like her mother was Sallie/Sarah Donavan, possibly the wife on John Donovan. You might try the free search tool at: https://familysearch.org/search and plug in the names of the various siblings to see if you can find Sarah's maiden name?
United States Census, 1920 Philadelphia Ward 31, Philadelphia, PA
Citing this Record: "United States Census, 1920," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/M6YR-4Z2, Catherine Morrison in household of William Morrison, Philadelphia Ward 31, Philadelphia, Pennsylvania, United States; citing sheet 4A, family 68, NARA microfilm publication T625, National Archives and Records Administration, Washington D.C.; FHL microfilm 1,821,635.
William Morrison Head M 42 1878 Pennsylvania
Catherine Morrison Wife F 37 Pennsylvania
William Morrison Son M 15 Pennsylvania
United States Census, 1910 Philadelphia Ward 19, Philadelphia, PA
Citing this Record: "United States Census, 1910," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/MG8T-V3N, William Morrison in household of William Morrison, Philadelphia Ward 19, Philadelphia, Pennsylvania, United States; citing enumeration district (ED) 320, sheet 9A, family 185, NARA microfilm publication T624, National Archives and Records Administration, Washington, D.C.; FHL microfilm 1,375,406.
William Morrison Head M 32 Pennsylvania
Catherine Morrison Wife F 27 Pennsylvania
William Morrison Son M 6 Pennsylvania
Sallie Donovan Mother-in-law F 61 Pennsylvania
United States Census, 1900 Philadelphia city Ward 23, Philadelphia, PA
Citing this Record: "United States Census, 1900," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/M3WW-QG7 , Kate Donavan in household of John Donavan, Philadelphia city Ward 23, Philadelphia, Pennsylvania, United States; citing sheet 1B, family 17, NARA microfilm publication T623, National Archives and Records Administration, Washington, D.C.; FHL microfilm 1,241,465.
John Donavan Head M 52? 56 June 1844?47 Ire married 30 yrs Naturalized 1855
Sallie Donavan Wife F 46 May 1854 PA 11 children 7 living
Ella Donavan Dau F 21 PA
Lizzie Donavan Dau F 19 PA
Kate Donavan Dau F 17 May 1883 PA
Gertrude Donavan Dau F 15 PA
Possible additional records at https://familysearch.org/search/record/results?count=20&query=%2Bgivenname%3Ajohn~%20%2Bsurname%3Adonovan~%20%2Bbirth_place%3AIRE~%20%2Bbirth_year%3A1844-1847~%20%2Bresidence_place%3APA%20%2Bresidence_year%3A1850-1940~%20%2Bdeath_place%3Apa~%20%2Bdeath_year%3A1900-1909~%20%2Bspouse_givenname%3A%22sallie%20sarah%22~