Cathy Foster said Diesel was 4 years old and was adopted along with another dog, Chelsea, for puppies.
"She was my sweetheart," Foster said. "She definitely was my sweetheart."
Foster's home burned down in March, and as a result, Diesel and Chelsea were staying with her daughter. On Monday, the dogs got loose.
"I'm not complaining about the dog pound picking them up, because that's the name of the game," she said. "Your dogs get out. They get picked up. You pay the fine."
Foster said she and her daughter made arrangements with the Harris County Animal Shelter to pick up the dogs last Friday.
"She even confirmed back to me that I would be there between 2 and 5," she said. "We'd be picking them up on Friday. Everything was fine."
But when she got to the shelter at her scheduled time, it was anything but fine.
"We could find Diesel, but no Chelsea," Foster said. "Then they're scrambling around with our paperwork. Nobody knew who had it, where it was at."
Then, she discovered Chelsea had been euthanized by mistake.
"He said they have a ritual they go through every morning," she said. "He said some dogs make the list, some dogs don't. And he said he could not explain why Chelsea was on that list...She should have never been on that list. She was accidentally put on the list."
The Harris County Animal Shelter declined a request for an interview to answer exactly how the mistake happened, but it sent a statement reading, in part:
"As a result of this incident, the appropriate employees have been disciplined. I have ordered a review of this event and we will implement additional employee training to prevent this from happening in the future."
But that's not enough for Foster.
"He said, 'If it makes you feel any better, there will be people fired,'" she said. "And I'm like, 'That's not gonna bring my dog back.'"
Foster is calling for better education for employees.
"It's a shame, you know, there needs to be a lot of difference in that facility," she said.
She's also pushing for a more streamlined workflow.
"They need to be higher educated on the jobs that they do," Foster said. "They're handling people's loved ones. It's not just animals they're there for."
Foster said she believes the staff is overwhelmed.
A spokeswoman for the shelter told Eyewitness News it is extremely overcrowded, and that they are currently holding about 500 animals. Their capacity is 150.