Her children were then aged 5, 3 and 5 months.
Ryan, Oakes' partner and the father of the children, initially denied a charge of murder but later pleaded guilty.
The court heard he was in a "pure, blind rage" after confronting Oakes following a night drinking in town.
When Oakes arrived home several hours after him, he beat and strangled her to death in the garage in a jealous fury.
At sentencing, the court heard from the Crown that Ryan punched Oakes in the mouth, puncturing her lip with her tooth and rendering her "senseless if not completely sense-less" before he strangled her.
Her children were sleeping nearby as she was murdered.
Ryan appeared before the Parole Board in May and the decision has been released to the public.
Ryan is now 50 and was known to authorities before the murder.
He had previous convictions for driving, unlawful possession of drugs and some violence - although Parole Board chairman Sir Ron Young said none were "especially serious" offences.
"We saw him last in May 2018. At that stage, he had had a number of misconducts in prison," Young said.
"There was concern about his consumption of drugs and alcohol and its relevance to his offending."
When last seen by the board, Ryan had completed one rehabilitation programme and was part way through a second.
However, he still had some aggressive and violent conduct within prison.
Young said since then, Ryan's conduct in prison had "significantly improved".
"And no criticism is made of it during the last six to nine months," he said.
"Mr Ryan has done eight one-on-one sessions with a psychologist ... [he] spoke very highly of the work he had done.
"It seems to us that the issue of Mr Ryan's rehabilitation has been thoroughly discussed and considered and it is now felt that all of the rehabilitation necessary has been completed".
Young said Ryan's focus would now shift to reintegration.
"We noted in our last decision that Mr Ryan had been turned down for the more liberal regimes of self-care and work outside the wire," he said.
"For perfectly understandable reasons, he asked and we in turn asked Corrections for them to tell Mr Ryan why he had been rejected in his application to go to that more liberal reintegration regime.
"It seems to us only fair that Mr Ryan is told why he has not been approved so that he can address whatever inadequacies there may be in his application."
Young said the board considered Ryan to be a " very thoughtful man".
"And an obviously intelligent man," he said.
"He has already himself prepared what seems to be an excellent safety plan.
"We encourage Corrections, therefore to work with Mr Ryan on reintegration.
"In the meantime, he remains an undue risk."
Ryan will next appear before the Parole Board in April 2021.
