Two Met Police officers, Pc Deniz Jaffer and Pc Jamie Lewis, later admitted sharing photographs of their bodies on WhatsApp.
They pleaded guilty to misconduct in a public office at the Old Bailey earlier this month.
The victims’ mother, Mina Smallman, told ITV’s Good Morning Britain: “We knew that this was going to happen, that was going to be the result, but our case is almost a test case because the sentencing happens at the Old Bailey on December 6.
“Now the issue is Jaffer had already resigned from the Met.
“Normally, there have been cases where they have refused them to resign, so the question is ‘Why have they done that?'”
She went on: “But I think it’s a starting point. I know the Met know they’re being watched, their every move, we’ve drawn attention to that.”
The two officers were assigned to protect the scene overnight after the sisters were found dead.
Instead, they breached the cordon to take “inappropriate” and “unauthorised” photographs of the bodies, which were then shared on WhatsApp.
Jaffer took four photographs and Lewis superimposed his own face on to a picture with the victims in the background.
Lewis, who used “degrading and sexist” language to describe the victims, also shared crime scene pictures with a WhatsApp group of 40-plus officers called the “A Team”.
Ms Smallman said: “As soon as I heard that, I said ‘This is not a one-off.’ You don’t start breaching your position with this being your first move. This is going to be much bigger.
“We were told it had been sent out to members of the public. So, at the point they were being investigated, they had sent it to a doctor and a dentist who were part of the WhatsApp group and the IOPC went to them and investigated them.”
She added: “It took me to the depths of darkness of how on earth could you do that? Up until that point I had never imagined what the girls’ dead bodies looked like, but now and since then I have flashes of what I think that picture is.”
Following the men’s guilty pleas, Met Commissioner Dame Cressida Dick issued a further apology to the family.
She said: “What former Pc Jaffer and Pc Lewis chose to do that day was utterly unprofessional, disrespectful and deeply insensitive. I know that is the view of colleagues across the Met who utterly condemn this behaviour.”
Speaking about the statement, Ms Smallman said: “I thought it was the worst presentation – she was shaking like a leaf, it was all scripted. This is the woman who’s going to tackle what we’re up against in the Met.
“I don’t think so. It’s time for her to go.”
A statement from Met Assistant Commissioner Helen Ball said: “Our thoughts are with the family and friends and we deeply regret the additional distress this matter’s caused them.
“We’re profoundly sorry personally and on behalf of the Met.”