But the turtle persevered, thanks to injections of antibiotics and a forced diet of squid. Somehow, she swam with just one flipper, even though she can only move in counterclockwise circles and has to push her now 10-pound body off the bottom with her head to breathe.
"The wounds have healed very nicely. The problem is she doesn't swim very well," said Jeff George, curator at the nonprofit Sea Turtle Inc., a 31-year-old turtle conservation facility that treats and returns injured sea turtles to the wild.
Now, her caregivers hope to make her what's believed to be the first sea turtle fitted with a prosthetic flipper.
Three-flipper turtles can return to the sea and two-flipper turtles can survive in captivity. But those left with only one after predator attacks or run-ins with boat propellers are usually killed.
Allison, named for the daughter of one of the tourists who found her, was spared because an intern begged for a chance to nurse her back to health the summer she was found. Since then, Allison has adapted and grown to normal size for her age.
"With Allison, from the day she arrived, she was a fighter," said Lucia Guillen, the nonprofit's resident biologist and educator.
But because an Atlantic green sea turtle like Allison can grow to 450 pounds and live a century or so, her long-term prognosis with only one flipper is not promising.
"She would be destined to shallow water for the rest of her life and that becomes a quality-of-life issue," George said.
That's when they got the idea for a kind of bionic turtle.
A group of veterinary and medical professionals - including an assistant professor at the world-renowned University of Texas M.D. Anderson Cancer Center and the UT Dental Branch in Houston - have volunteered to help fit a prosthetic flipper to her left rear side.
She has a small bony stump there that could help hold a fake flipper, while making it difficult for her to use her clamping jaw to rip it off. Allison may have been the victim of a shark attack.
University of Texas' Dr. Sudarat Kiat-amnuay plans to develop a prosthetic using the same kind of silicon she uses to create facial prosthetics for humans. Her dental expertise helps because the kind of tiny hardware used in dental implants are probably the best size match for Allison's bones.
Kiat-amnuay plans to use the same technique she would to create a prosthetic nose or ears for a human patient.
She'll use sculpting wax and molds created from a dead turtle's flipper and then custom fit one for Allison. The silicon, now only tested in saliva, will be tested in sea water to make sure it holds up, she said.
Kiat-amnuay said she even plans to hand color the fake to match Allison's natural flipper.
The first trial flipper could be ready within a few weeks, though Kiat-amnuay and Sea Turtle Inc.'s veterinary director are still figuring out how to attach it.
It may seem silly going to so much trouble for a turtle, but Allison would not be the first animal to get a prosthetic replacement. At least two dolphins, one in Japan and one in Florida, have successfully been fitted for prosthetic body parts.
Kiat-amnuay said part of the appeal is being the first to do so.
"It will be interesting and it will be fun," she said. And "if you're able to work on her, you may be able to apply it and work on more turtles."
Guillen, who initially thought Allison should be put down, said the work on her now might help others, especially because sea turtles missing even a single flipper are far less likely to successfully reproduce.
"If we can do something for other turtles, then keeping her alive is worthwhile," said Guillen. "We're hoping we can accomplish something with Allison that will benefit other turtles."