He said she was inexperienced and her bosses had failed to supervise her.
The probation officer has name suppression and Mr Henry declined to comment further on the allegation outside court. He said all would be revealed at the defended hearing, likely to be next year.
"There's a long way to go but she wants her day in court. She wants to expose what happened to her.''
Outside court Ms Couch told APNZ: "I'll just say that I'm looking forward to my day in court and I'm hoping for a jury.''
She declined to comment further.
In court Mr Henry argued the matter was straightforward enough for a jury to understand.
However Victoria Casey, the lawyer representing the Attorney General, said a jury would need to consider complex issues that were affecting the probation service at the time of the killings.
"There are complicated factual matters which will involve complicated exploration by experts.''
Ms Casey said the hearing would take upto eight weeks before a judge alone and "significantly'' longer if a jury was involved.
Justice Timothy Brewer reserved his decision and said he would need to consider rulings on the case from the Court of Appeal and the Supreme Court.
The Supreme Court ruled in 2010 that Ms Couch could sue for damages for negligence and personal injury but there would be a high test for the claim to succeed.
Bell murdered William Absolum, 63, cleaner Mary Hobson, 47, and garage door installer Wayne Johnson, 56, when he went into the RSA to steal $12,000.
All three were bludgeoned with a blunt weapon and one was also shot at close range during what police described as one of the most violent robberies in New Zealand's criminal history.
Bell is now serving a life sentence with a non-parole period of 30 years for the murders and the attempted murder of Ms Couch.