Names match, but perhaps the girls adjusted their ages ?

http://www.census.nationalarchives.ie/pages/1901/Waterford/Waterfor...
Farrell Mary M 65 Female Head of Family Roman Catholic Waterford House Holder Read and write - Widow -
Farrell Kate M 29 Female Daughter Roman Catholic Waterford Milliner Read and write - Not Married -
Farrell Mary B 29 Female Daughter Roman Catholic Waterford No Trade Read and write - Not Married -
Farrell Alice 27 Female Daughter Roman Catholic Waterford Telegraphist Read and write - Not Married -
Farrell Frances M 19 Female Daughter Roman Catholic Waterford No Trade Read and write - Not Married