CLARKSVILLE, Tenn. (WKRN) — The pain of not knowing what happened to a missing loved one is hard to imagine by those who haven’t experienced it. For one Clarksville family, that pain has lingered for more than 18 years.

“She loved music, she loved to dance, she loved to go for walks, wasn’t real, real sociable. She loved me, I was her only child and I was pretty much her world,” Connie Diffenderfer told News 2’s Nikki McGee.

Diffenderfer was talking about her mother, Mary Alice Cox, who disappeared almost two decades ago.

Cox, who struggled with mental illness, was 54-years-old when she was living in a group home on Vivian Drive in Clarksville.

The case hasn’t been talked about often, but for Diffenderfer, it has always been top of mind.

“She wasn’t at her best, but she also wasn’t psychotic the day that I talked to her, she was completely fine as far as being able to have a conversation,” Diffenderfer remembered.

On March 20, 2004, Cox went to buy cigarettes but never returned.

“I just expected her to walk to the market, get her cigarettes, and come back and I’d talk to her the next day,” said her daughter.

About two weeks later, Cox’s purse and medication were found along the Cumberland River near Stewart County. She was previously diagnosed with COPD and relied on intermittent oxygen.

“She would have had to have sought medical care to be able to breathe. She needed oxygen to be able to do that,” Diffenderfer continued, “I know something happened to her. I just don’t know what.”

Diffenderfer believes her mother got a ride from someone who didn’t take her home.

“If I let myself go there, it’s devastating because I don’t know if she was hurting, I don’t know if she was afraid, alone, and I know she would be thinking about me,” she said.

Cox’s disappearance has gone cold for Clarksville Police. Anyone with information, no matter how insignificant it might seem, is urged to come forward.

“Mothers Day comes around, her birthday comes around, the date that she went missing comes around… to be able to not even know how to respond because you just don’t know what happened,” her daughter reflected.

Tips can be submitted anonymously by calling Clarksville Crime Stoppers at 931-645-TIPS (8477).