Ruddelle claims she acted in self defence trying to protect herself and her teenage son, and was suffering from social entrapment, or battered women's syndrome, after a lifetime of domestic violence - including at the hands of Ngapera.
The trial is in its second week.
Today the jury heard evidence for clinical psychologist Dr Alison Towns.
Towns specialises in population based approaches to the prevention of domestic violence and has a particular interest in the ways "mechanisms of power are utilised to maintain silence and prevent action to stop such violence".
She met with Ruddelle on several occasions and interviewed her about the alleged murder and her life.
"I was asked to determine the nature of Ms Ruddelle's relationship [with] Mr Ngapera, whether there was domestic violence involved and whether it took the form of social entrapment, whether that was present," she said.
Towns said Ruddelle told her that at times Ngapera could "lift her mood" but at other times there was "a difficult side to him".
"She mentioned that he had killed somebody in Australia … and she took this to mean that he could kill someone," she told the court.
"He could be lovely when he wasn't drinking but she found him quite threatening when he had been drinking."
Towns was aware of the 16 times Ruddelle had called police about Ngapera in the lead-up to his death.
She was also aware of the examples Ruddelle had given the court earlier in the trial about Ngapera's frightening behaviour.
"She spoke of the relationship being punctuated by episodes of physical violence," she said.
"Ms Ruddelle spoke of him coming home and telling her that a taxi driver had tried to rip him off and he had 'smashed him' or hit him.
"In the morning when he woke up ... He'd come to her and accused her of having pushed him out of bed and punched her in the head two times.
"I would see a punch in the head as being quite a dangerous thing ... that's actually quite a dangerous action."
Towns said Ngapera's behaviour indicated clearly that there was social entrapment, intimate partner violence and coercive control.
She referred to the time that Ngapera choked Ruddelle, holding her against a wall by her neck until the woman thought she was going to be killed.
"She spoke of being strangled which is a really dangerous form of violence," Towns said.
"Women who are strangled are more than seven times more likely to die in domestic violence."
Towns was aware that Ruddelle had been granted a protection order - and that it was discharged on her request soon before he died.
"It's important to understand that it's not the victim who makes a decision to discharge a protection order, that's something a judge does," Towns said.
"She has to apply for it and then someone else makes a decision whether that order is discharged.
"Protection orders really do make women feel safer, so it's likely that does assist in decreasing the violence," she said.
"I'd suggest to you that there's potential for her to feel less safe once the protection order was discharged."
Towns said some of the violence Ruddelle had been subjected to would have been "threatening and quite a scary experience".
She said Ruddelle also would have been intimidated.
The woman left her home after one incident and lived in her car for a short time with her teenage son to get away from Ngapera.
She also reached out to Women's Refuge for help.
Towns said Ngapera was bigger than Ruddelle, making it easier for him to "exercise control" over her.
"There are quite a lot of indications of Mr Ngapera using threats or coercion," she said.
"She said he was scary when he drank alcohol ... and that's why she tried to protect her children when he drank."
Towns said Ngapera would verbally abuse Ruddelle and call her names.
"That is consistent with emotional abuse," she told the court.
Towns said Ngapera also tried to "isolate" Ruddelle, which was common in the realm of intimate partner violence.
"The male partner will sometimes, actually quite commonly, try to distance the woman from her children and her friends ... Miss Ruddelle said Mr Ngapera would try and stop her from seeing her children and that was a source of arguments for them.
"She was quite distressed by that, she liked to have her children around.
Another form of coercive control was Ngapera being angry at Ruddelle for getting a protection order - effectively blaming her for his abusive behaviour.
Towns gave the jury her professional opinion on the matter.
"Ms Ruddelle would have experience coercive control ... intimidation threats, stand-over tactics
"She's had emotional abuse, he's tried to isolate her from her family ... Those all add up to, in my opinion, that she's experienced coercive control."
The fact Ruddelle was Māori also played a part.
Her culture meant showing compassion, kindness, empathy and hospitality was "very important" which is why Ruddelle was determined to stay with Ngapera and help him.
The accused told the court earlier that she loved Ngapera and wanted to heal him and marry him.
"I think there's pressure on Māori women in this context to nurture and take care of people," Towns said.
Towns told the court that Ruddelle's childhood and abusive relationships before she met Ngapera also had "a profound and prolonged" effect.
"My opinion is that she's experienced social entrapment and her experience are consistent with victims of domestic violence," she said.
"She has shown some of those symptoms (of PTSD).
"PTSD is the primary mental health impact from domestic violence ... she's experienced feeling like she had to be on alert all the time which is consistent with post traumatic stress.
"She has avoided having to talk about things that are difficult for her, and she [has] spoken about being ashamed and embarrassed.
"My opinion is that she does have some symptoms consistent with PTSD and that would be consistent with the domestic violence she's experienced.
"She's had a lifetime of trauma really ... we know that prior to her relationship with Mr Ngapera she's attended refuge, so she's had a lot of trauma.
"When you get an accumulative lot of trauma it affects how you respond ... it makes it much more easy when you feel threatened to flip into survival mode.
"That's not a rational part of the brain, it's very instinctive ... it will throw you into a fight, flight or freeze ... If you've got past experiences of trauma when you're under threat you're going to be more readily triggered."
Towns said Ruddelle remaining in the home the night Ngapera was killed, rather than running, was in line with her past trauma.
"That would be consistent with a freeze response ... that would be consistent with a survival response.
"She would have been triggered into survival."
Yesterday the jury heard from Rachel Smith, an independent family violence consultant who has worked extensively in New Zealand and the UK with victims and agencies.
Smith gave the jury an insight into intimate partner violence - and social entrapment.
The trial, before Justice Matthew Palmer, continues.
DO YOU NEED HELP?
If you're in danger now:
• Phone the police on 111 or ask neighbours of friends to ring for you.
• Run outside and head for where there are other people.
• Scream for help so that your neighbours can hear you.
• Take the children with you.
• Don't stop to get anything else.
• If you are being abused, remember it's not your fault. Violence is never okay
Where to go for help or more information:
• Shine, free national helpline 9am- 11pm every day - 0508 744 633 www.2shine.org.nz
• Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz
• Shakti: Providing specialist cultural services for African, Asian and middle eastern women and their children. Crisis line 24/7 0800 742 584
• It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz
