She saw the victim emptying the rubbish outside and Mason attacked her.
The victim, who was in hospital for seven days with injuries including a fractured skull, had recurring headaches and nightmares and ongoing fears for her personal safety, which seriously affected her ability to work.
Mason told Judge Ingram she felt bad about what she did.
"But I could not handle what my husband and [the victim] did. I couldn't face it going on. Their adultery was just too much to take," she said.
"I went around there to visit my husband, and when she [the victim] walked out the door I was shocked and just reacted without thinking," Mason said.
"I'm sorry matua that I will end up in jail for this stupid act but I can't at this point feel sorry for [the victim] or forgive her or my husband for the adultery.
"I want counselling and God willing I will get the help I need," she said.
Mason said the day before the assault her husband told her he loved her and wanted to sort things out with her.
"It destroyed me, matua. Adultery is not right in the eyes of God," she said.
Mason's lawyer, Rachael Adams, urged Judge Ingram to take into account her client's "unfortunate and tragic" background and long-standing mental health difficulties.
There was no evidence this was a premeditated attack, and Mason had "lost control" on seeing the victim walk out the door rather than her husband, she said.
Judge Ingram said he understood Mason's feelings of jealousy and wanting revenge but this was serious offending which could only ever result in a prison sentence.
Given the victim's age and stage of life, this was a "devastating attack" and the consequences would likely "never leave her for the rest of her life", he said.
However, the judge said he was prepared to accept this was a spur-of-the-moment assault, and Mason genuinely regretted her actions, albeit she did not feel sorry for her victim yet.
Judge Ingram said he was prepared to take into account Mason's difficult background and her mental health issues had clearly seriously impaired her judgment.
The victim's injuries included:
A fractured right eye socket with an inner-eye cut, minor skull fracture behind her left ear, an injury to left ear, a broken left thumb; fractured right hand, a hole in the left side of her face, an open wound on her left thigh, surface wound on her left arm and significant bruising, including on her shoulders.