Marie McCourt said she hopes someone will now come forward and tell her where her daughter’s body is buried.
A murder victim’s mother who campaigned to bring in Helen’s Law has described the death of her daughter’s killer as a “great relief”.
Reports have said Simms died last week.
The PA news agency understands no cause of death has yet been given.
Mrs McCourt, 从 St Helens in Merseyside, told the Mirror: “It’s a great relief knowing that this man is at last wiped off this earth.
“He’s got what he deserved.
“I’m hoping now maybe he spoke to somebody in prison or maybe one of his friends or family who were perhaps too scared to come forward when he was alive, will do so now.
“I just pray now that somebody may have some details of where he said he had done it.
“It breaks my heart but not just mine but all families who’ve had loved ones taken.
“It’s hard to lose a child through illness, it’s worse when someone deliberately takes her life.”
She added that she lived in fear when he was released from prison with a tag on in 2020.
Insurance clerk Ms McCourt was 22 when she vanished on her way home from work in 1988.
Mrs McCourt’s campaigning following her daughter’s death led to the Prisoners (Disclosure of Information About Victims) Act, dubbed Helen’s Law, being enacted in 2021.
The law makes it harder for killers and paedophiles who hold back information on their victims to receive parole.
Under the legislation, killers could still be released if no longer deemed a risk to the public even if they refuse to disclose information.
But the Parole Board will be legally required to consider whether they have co-operated with inquiries as part of their assessment.
Pub landlord Simms was handed a life sentence in 1989 after being convicted by a jury on overwhelming DNA evidence of Ms McCourt’s abduction and murder.
He always maintained his innocence, despite never saying where he hid her body.