Marie McCourt said she was "in shock" when she learned of Thursday's ruling on Ian Simms, who was convicted by a jury three decades ago on overwhelming DNA evidence of abduction and murder.
The pub landlord has always maintained his innocence over the death of the 22-year-old insurance clerk, who vanished on her way home from work in Liverpool in 1988 and whose body has never been found.
Ms McCourt, from Billinge, Merseyside, has fought tirelessly to keep killers behind bars until they lead police to the victim's body, but her campaign - dubbed Helen's Law - failed to be ratified before Parliament was dissolved.
She is now considering challenging the Parole Board's decision in the High Court but said such action "could be expensive" and she needs help after she said she had "never received a penny of legal aid".
In a statement issued through fundraising website GoFundMe, she said: "I have been staggered and overwhelmed at the outpouring of support I have received since the Parole Board's decision to release my daughter's killer was announced.
"My legal team is now considering what avenues are open to me to stop the release; one such option is to launch a judicial review of the decision in the High Court.
"Taking action could be expensive - which is why I am launching a crowdfunding appeal.
"The Parole Board has acknowledged that Ian Simms, who murdered my daughter in February 1988, will never reveal the whereabouts of her body - yet still think him fit to be released.
"What message is this giving to other killers who have acted in this way? Stay silent, continue torturing the family, and you'll still walk free?
"I am making a stand not just for Helen - but for every other missing murder victim out there. I want to ensure no other family goes through this ordeal."
The final decision on when Simms is released will be made by the Prison Service, although there will now be a three-week period during which either the Justice Secretary or even the killer himself can appeal.
The Parole Board explained Simms was deemed suitable for release due to factors including the "considerable change in his behaviour".