For years, "Nashville" star Kimberly Williams-Paisley has had to watch her mother succumb to primary progressive aphasia, a form of dementia for which there is no cure.

Williams-Paisley,whose credits include the film "Father of the Bride" and in the the ABC hit series "Nashville", discussed her mother's struggle in an interview this morning with " Good Morning America" co-host Robin Roberts.

Williams-Paisley, who is married to country music star Brad Paisley and has two children, explained why she's now talking about what her mother faced.

"I'm finally at a point - my mother's finally at a point where I feel like it's OK to talk about it. There was a long time … that she didn't want us to talk about it, and that was so much a part of the stress of what we were all going through, was that we had to hide it and cover up for her, and protect her pride," she said. "And I just felt like we were at a point where our story could help other people."

Williams-Paisley writes about the plight of her mother, Linda Williams, in the March issue of Redbook magazine, on newsstands now. She says her mother started showing symptoms about two years before she was diagnosed at age 61.

"It seemed stress related," Williams-Paisley, 42, recalled. "It seemed that she had more anxiety. It seemed that she was fighting to find words more than she used to. But it was actually my mom who came to us and said, 'Something's wrong.' I'm having trouble finding words. I'm having trouble writing my name on my checks at the grocery store.'"

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"I'm finally at a point - my mother's finally at a point where I feel like it's OK to talk about it. There was a long time … that she didn't want us to talk about it, and that was so much a part of the stress of what we were all going through, was that we had to hide it and cover up for her, and protect her pride," she said. "And I just felt like we were at a point where our story could help other people."

Williams-Paisley said her mother started showing symptoms about two years before she was diagnosed.

"It seemed stress related," Williams-Paisley recalled. "It seemed that she had more anxiety. It seemed that she was fighting to find words more than she used to. But it was actually my mom who came to us and said, 'Something's wrong.' I'm having trouble finding words. I'm having trouble writing my name on my checks at the grocery store.'"

It was her mother convinced the family that it was time to get tests done.

"We didn't even know that they were - they were going through these tests for months. And then they sat us down on Christmas and told us that - what her diagnosis was, and that it was going to be five to seven years before she'd need full-time care. And she's pretty much been right on schedule," Williams-Paisley said.

"And we didn't even know that they were - they were going through these tests for months. And then they sat us down on Christmas and told us that - what her diagnosis was, and that it was going to be five to seven years before she'd need full-time care. And she's pretty much been right on schedule," Williams-Paisley said.

"My dad was in the midst of it … and it's very dangerous for the caregiver," Williams-Paisley said. "And people don't always realize that. And I know my dad didn't realize it in the depths of where he was. It's hard - it was hard for him to see the truth that we saw, that he was withering away.

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"We finally convinced him that she needed to be put into a long-term-care facility," she added. "And so I mean, I would just say to people going through it to keep an eye on the caregiver."

For the five years after her mother's diagnosis, her mother had her own communication with Williams-Paisley's children.

"When I found out what her diagnosis was, I thought, 'Wow, she's just not going to know my kids.' And what was so cool was seeing how she actually really did interact with my kids … You know, both down on the floor being really goofy and silly. And my kids adored her … they played really well together," she said.

She'll hang on to those moments, now that her mother is no longer the woman she knew.

"What I had to come to is being able to let go of the mother that I grew up with, because she's not there," Williams-Paisley said. "And the pain came from looking at the person that's there now and comparing it to who was there. That's painful.

"But if I say goodbye to that person who doesn't exist anymore and say hello to this person that I still have a bond with, it's much easier to love her and to be with her," she added.

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She's had to learn new ways of communicating with her mother.

"My mom used to be very articulate, and was one of the best listeners in our family. And so communication with her now is very different. She communicates on an emotional level. And music is a very effective way of communicating with her," she said. "I was just with her yesterday, and when I sang a song that she knew, her face would light up. When I sang a song she didn't know, it wouldn't."

She said it was interesting to find that there were still some memories that her mother retained.

"That's the way of saying, 'Hey, remember those days when we used to, you know' … It's through a song. 'Remember when we used to sing this?' And that's a way of engaging with her," she said.