Whole-life prison sentences will become the "default" punishment for "sexual or sadistic" murders, the prime minister has said.
She is only the fourth woman to be given a whole-life tariff in England and Wales. Sixty-six men are currently serving them in prisons and secure hospitals across the two nations.
But the government says it plans to change the law so that "judges are required to impose whole-life orders on the most depraved killers, except in extremely limited circumstances".
Justice Secretary Alex Chalk said: "A whole life order will now be the expectation for murderers where the killing involves sexual or sadistic conduct."
The proposed change in legislation will give judges "greater confidence to hand out whole-life orders without a risk of challenge in the Courts of Appeal", according to ministers.
Under changes to the Police, Crime, Sentencing and Courts Act, which came into effect last year, the criteria for whole-life tariffs was expanded to include premeditated murders of children.
But now "sexually-motivated" murders will also merit the most severe sentence.
New criteria could have applied to Aleena and Nessa cases
Jordan McSweeney was jailed for life with a minimum of 38 years for the murder of Ms Aleena in Ilford.
While Koci Selamaj was handed life with a minimum of 36 years for killing Ms Nessa in Greenwich.
Sentencing him, Lord Justice Fulford said the seriousness of Couzens' crimes and the "misuse of a police officer's role" was so "exceptionally high" that they merited a whole-life tarriff.
Rishi Sunak commented: "I have shared the public's horror at the cruelty of crimes we have seen recently.
"People rightly expect that in the most serious cases, there should be a guarantee that life will mean life. They expect honesty in sentencing.
"By bringing in mandatory whole life orders for the heinous criminals who commit the most horrific types of murder, we will make sure they never walk free."
Shadow justice secretary Steve Reed MP said Labour would not take "any lessons from this soft on crime Tory government".
"Under their watch, nine out of ten crimes go unsolved and tens of thousands of dangerous criminals including gunmen, child abductors, and sex offenders have avoided jail sentences," he said.
"To make matters worse, our prisons are now full because they failed to build the prison cells we need, forcing judges to hand out softer sentences."
He added that if elected, Labour would "implement tougher sentences for dangerous criminals and build the prison places to put them behind bars".