He also admitted a minor charge of operating a motor vehicle recklessly, as he tried to evade police before being arrested after a five-hour stand-off.
Some of Ms Farrall's devastated family members were in court to see McDonald on the AVL screen wearing green prison clothes and saying, "Guilty your honour".
He also lost his name suppression and will be sentenced on July 24.
McDonald was on parole at the time of the crime spree, a Parole Board decision shows.
He had been sentenced at Palmerston North District Court in May 2009 to five years and three months in custody for multiple crimes, including the manufacture of methamphetamine, burglary, theft and arson.
Jeremy Lightfoot, National Commissioner of Corrections Services today said initial inquiries showed that McDonald had met his parole conditions up to the point of his last reporting to them on March 18 this year.
"Our probation staff were in regular contact with him and those he was living with," Mr Lightfoot said.
A comprehensive review of his management is now being undertaken "to ensure his supervision in the community met all our standards and expectations", he said.
"This comprehensive review is not complete yet, and as we will also be giving advice in regards to sentencing options for this offender it would not be appropriate for us to comment before he is sentenced."
A hearing at Rimutaka Prison last September was told McDonald was a self-confessed alcohol and methamphetamine user who smoked cannabis daily since he was 15, but his risk to the community over the remaining nine months of his sentence could be "adequately mitigated".
He told the board that he had accommodation available in Christchurch.
"There is, however, no work available there, although he has tentatively proposed that in time he may work with a friend in Christchurch. This seems to be some way off at the moment," the decision said.
