The tragic murder-suicide unfolded on Friday night in Sudden Valley, according to the Whatcom County Sheriff's Office.
Deputies performing a welfare check at the family's home discovered the bodies of 55-year-old Michele Boudreau Deegan and her daughters the following afternoon after a person living in the multi-level residence reported that they were dead.
An initial investigation revealed that Deegan had been embroiled in a custody dispute over the children, which was believed to be her primary motive in the shootings.
Michele Boudreaux Deegan shot her seven-year-old twin daughters before turning the gun on herself at the family's home in Sudden Valley, Washington, over the weekend, police say
Investigators said Deegan killed her daughters (pictured) while they slept on Friday night
Deegan worked as a psychotherapist, according to her website.
The front page of the site reads: 'My goal is to teach clients new ways of perceiving their problem, healthy coping behaviors for responding to their problem, and healthy attitudes & communication skills for working with their families, partners, or work environment so they can make changes in their own life.'
Friends said Deegan adored her children but suffered from mental health issues
On the day of the shootings, Deegan shared a number of articles about 'narcissists' on her professional and personal Facebook pages - including several related to parenting and a few about how people in relationships with narcissists can be driven to suicide.
A person who knew Deegan described her as 'deeply troubled' and told KIRO 7 that they had contacted child welfare authorities with concerns about the twins before their deaths.
Neighbors told the TV station that the twins were rarely seen outside their home.
'Really right now, I'm just in shock I can't believe this happened,' one neighbor said.
Whatcom County Sheriff Bill Elfo said: 'It's a real tragic situation that we're still investigating, trying to get more information on what might have motivated someone to do something this horrific.'
Deegan had been embroiled in a custody dispute over the children, investigators said
Deputies performing a welfare check at the family's home (pictured) discovered the bodies on Saturday afternoon
One of Deegan's friends reacted to the news in a Facebook post, saying that she was 'mentally ill'.
'Michelle was a wonderful woman....she HAD TO HAVE BEEN trying (in an absolutely sick, unimaginably twisted way, obviously) to "protect" the girls from a life with their dad without her,' the friend wrote.
'She was a kind and warm friend, bright and empathetic, a psychologist with a local practice that helped so many people, including me, and my daughter.'
The friend confirmed that Deegan was in a 'horrific custody battle, with a man she had a domestic violence protection order against'.
'Every time she believed her divorce was almost final, she would be dragged into a new frivolous and expensive renegotiation,' she wrote.
'She had been bankrupted by litigation, right or wrong, she worried for her girls with their dad.....(the sad irony is not lost on me)......this was a mental health tragedy, not a terrible person.'
The friend concluded: 'I just really want everyone to know that Michelle did NOT abuse the girls, she loved them. She was just sick....and scared.