"How is it possible this can happen?" she asked.
"Now I never feel safe ... nobody deserves this."
Corrections southern regional commissioner Ben Clark said he wanted to extend a "sincere apology" to the victim.
"I can only imagine how distressing that this would have been," he said.
"The deputy prison director has also tried to make contact with the victim today to personally apologise and advise her of the action we have taken to prevent this from happening again."
It was only after inquiries were made by the Otago Daily Times this week that Corrections took action to contact the victim.
That is despite her informing police of receiving Hepi's unwanted contact a year ago, when it happened.
Corrections said it resulted in an alert being loaded in the system to stop a repeat incident.
Why no such alert existed in the first place was not addressed.
The court heard at sentencing that Hepi had served prison time for rape in the past, as well as for child sexual abuse.
He was subject to an extended supervision order - which included GPS monitoring - at the time of last year's kidnapping ordeal, but had breached it repeatedly.
Two psychologists found Hepi exceeded the threshold for psychopathy and Justice Robert Osborne said the man met the threshold for preventive detention "by a clear margin".
Clark said the ability for prisoners to send and receive mail was "a statutory minimum entitlement" and that about 15,000 letters were sent each week.
There was no recording of senders or recipients, he said, therefore they were unable to determine how many letters Hepi sent or whether he sent them himself, or had another person do so on his behalf.
This Dunedin case followed Corrections last week releasing results of an independent review into the prisoner-mail system, prompted by a departmental botch involving communications sent out by the Christchurch mosque accused.
Changes to prison mail system
• Regular audits of mail processes, including how staff make decisions to withhold or release mail.
• Setting up dedicated mail-monitoring teams to open, read and withhold mail.
• Providing interim guidelines on scanning and withholding mail, gang mail and content of a sexual nature.
• Outgoing envelopes identified as prisoner mail and contain contact details for recipients to contact Corrections if unwanted.