"I can't quite wrap my head around it and I don't know that I ever will. That she left the way she did," she tells PEOPLE. "That's how baffling and cunning mental illness is. You have to make peace with the fact that you don't know. Sometimes there are no answers."
Naomi "was always so determined. No matter what happened to her," her daughter says. "Being fired. Being forgotten. A single white female raising two babies by herself. On welfare and food stamps. She never gave up."
"So think about that and apply it to every stinking part of life, including death," Wynonna, 58, continues. "With the same determination she had to live, she was determined to die. It's so hard to comprehend how someone can be so strong and yet so vulnerable."
Jim Wright Wynonna Judd
In her grief, Wynonna did what she knew best: "Just go to the next step. Then go two more. Sometimes that's enough." That meant returning to the music she and her mom had loved making together and going forward with The Judds: The Final Tour.
It was a reunion they had planned to do together — but now Wynonna is singing alongside some of country's biggest names, including Faith Hill, Martina McBride, Little Big Town and Trisha Yearwood, in celebration of her mom's life and legacy. "I have to celebrate the joy as much as I can," she explains. "That's part of the reason I'm doing the tour."
Watch the full episode of People Cover Story: Wynonna Judd below or on the PeopleTV app.
In the weeks leading up to Naomi's death, Wynonna had been touring with her husband, drummer Cactus Moser. "It was incredibly painful for [my mom] because her favorite place to be was on the road and to be with me and [my sister] Ashley," she says. "She was by herself a lot. And so we were disconnected. One of my regrets is that I was so busy. She often talked about how lonesome it is in that house without us."
Jim Wright Wynonna Judd on the cover of PEOPLE
The last time Naomi and Wynonna saw one another was at the April 11 CMT Awards, where they sang their hit song "Love Can Build a Bridge." "The last thing I said to her was 'I love you,' and I'm so grateful for that," Wynonna says.
"I've accepted it as much as I possibly, humanly can," she explains of her mother's unexpected death at age 76. "Acceptance and then surrender, and what comes after is finding meaning."
Wynonna hopes she can help others by speaking out. "There is not one person on this planet that is not susceptible to some form of depression," she says. "The ones who need or want help, some will ask for it and some won't."
The Tyler Twins Naomi and Wynonna Judd
Throughout, the singer says, she has learned to remember compassion. "I have a saying that was on a t-shirt my mom wore in the '70s that said, 'Keep on Truckin.' You wake up in hell? Keep on truckin' — and now I'm walkin' it. When you deal with suicide, there is so much mystery there. What was she thinking in her final moments, what drove her to say I'm done? She's a tough son of a bitch. Yet she was done and she was in too much pain. I don't know what to do with that except to have compassion."
And so Wynonna continues to find strength in her family, her faith and music, the very thing that had so deeply connected the mother and daughter duo.
"I will take every available opportunity to celebrate life because everything is a gift in this life," she explains. "Your breath, your heartbeat, the next day. Maybe her greatest legacy was in darkness, there is light."
Jim Wright Wynonna Judd
For all the details on Wynonna Judd's journey through grief, pick up the latest issue of PEOPLE, on newsstands everywhere Friday.
If you or someone you know is considering suicide, please contact the 988 Suicide and Crisis Lifeline by dialing 988, text "STRENGTH" to the Crisis Text Line at 741741 or go to 988lifeline.org.
If you or someone you know needs mental health help, text "STRENGTH" to the Crisis Text Line at 741-741 to be connected to a certified crisis counselor.