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HIGH RIDGE, Mo. (CBS Local) — A dog who was recovering nicely from a rare kidney transplant from one of her puppies mysteriously died Saturday, Dr. Shannon Flegle, her veterinarian and owner, confirmed to CBS Local.

Star the dog received the transplant Oct. 10 after she was reunited with one of her pups, a daughter named Elsa. Star’s recovery was going well, according to Flegle, when exactly a month later, on Nov. 10, she suffered some kind of emergency and passed away within an hour.

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“It was very sudden and unexpected. … We are in shock and devastated beyond words,” Flegle wrote on a Facebook page she set up to update the public on Star’s progress. “We do not know exactly what happened, but think it was a reaction/toxicity to the anti-rejection medications that caused a chain reaction in her body.”

Fortunately, Elsa is doing “fantastic,” Flegle said.

Star’s incredible journey goes back three years when she was found with a litter of puppies in a plywood box on a hot summer day. She had just after given birth to 13 pups — nine survived — and had no food or water. The puppies were OK, but she was severely dehydrated and undernourished.

Star was nursed back to health and adopted by Dr. Shannon Flegle, Star’s veterinarian and owner of Murphy Animal Hospital in High Ridge, Missouri, just southwest of St. Louis. The pups also found homes, many in the local area.

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Everything was fine until last summer when Star began vomiting and stopped eating. Tests showed Star’s kidneys were failing.

Flegle said she gave Star intravenous fluids and supplements and also tried acupuncture. But when those treatments didn’t work, she began to consider more extreme options like dialysis and a kidney transplant, both of which are rare for dogs.

Flegle said she reached out to the Murray family, who had taken in Elsa, one of Star’s daughters. She tearfully explained that Star was sick and needed a kidney transplant.

“I could tell this was a mom, this was her baby, you know,” Jenny Murray told KTVI. “She was going to do what she needed to do to save her baby.”

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Murray discussed the risks and benefits with her husband and three children and they decided to help.

“This is Elsa’s chance to save her mom,” Murray said to her kids, “and they’re like, ‘Oh, so she’s a hero!'”

Surgeons at the University of Wisconsin-Madison performed surgery on on Oct. 10. Star’s blood work was back to normal within 36 hours and mother and daughter were soon back home recovering.

Flegle says she hopes Star’s experience “helps with future kidney donations and not the opposite.”

“We knew that the drugs would be our biggest hurdle and for some reason Star was very sensitive to them,” wrote said. “She fought so many other obstacles in her life so hard, but her body could not handle this one.”

Flegle told CBS Local the surgeons who performed the transplant are talking to experts across the country to try to figure out exactly what happened.

They are also hoping to set up a registry to facilitate lifesaving transplants for dogs.

“We are so thankful to have Star in our lives for the past 3 years,” wrote Flegle. “She gave us so much more than we could ever give her.”