MacDonald said she had no idea who would want to harm her daughter and described her death as a huge loss.
She had not seen her daughter for more than a year.
Duffin called on people to come forward to help end the mystery of why their kind-hearted niece and daughter was killed.
"You know who you are and other people know who you are.
"Just please, come forward. We're just calling on your consciences to try and put yourselves in Cathrine's shoes and the family's shoes and just what this is doing to everybody."
The detective in charge of Operation Archer, Glenn Barnett, said a team of 10 was dedicated to finding the killers.
Police were systematically working a number of areas of enquiry, including people of interest and information gleaned from police sources.
CCTV footage from near Tolley's Ward St home was being viewed.
"The footage we have reviewed so far is helping us to reconstruct the events of the night Lois was killed," said Barnett.
Police were still open-minded about the motive and appealed for those who may have had a lesser role in the attack to come forward in confidence.
He also appealed to parents who may have noticed a family member's behaviour change since the December 9 attack to come forward.