(CNN) -- An 8-foot-long alligator sank its teeth into a 90-year-old woman's leg and tried to drag her into a canal in southern Florida, a spokeswoman for the state's Fish and Wildlife Conservation Commission said.

Margaret Webb was walking in her flooded yard Wednesday in rural Copeland, Florida, about 80 miles west of Miami, when the alligator lunged at her and grabbed her by her left leg, commission spokeswoman Gabriella Ferraro said.

Dewain Daniels, who was driving by, stopped to help the woman, Ferraro said, and pulled her out of the water away from the alligator. But that didn't stop the huge reptile, which tried to come out of the water three times.

Daniels shot the alligator between the eyes with a .22 Magnum rifle, according to the incident report from the wildlife commission, and it retreated into the water.

Webb was airlifted to Lee Memorial Hospital in Fort Myers, where she's in critical condition after having her left leg amputated below the knee, Ferraro said. She's also being treated for a bite on her right leg.

Ferraro said alligators are the most active at this time of year, while water levels are at their highest, but unprovoked attacks are rare.

In 2010, the Florida Fish and Wildlife Conservation Commission reported six unprovoked attacks in the state.

Ferraro said the elderly woman, whose home is next to the Florida Everglades, is no stranger to alligator attacks.

"There are reports she has lost pets to alligators," she said.

Two wildlife officers and trapper David Regel returned to the site of the attack early Thursday morning to search for the alligator in the canals surrounding Webb's home.

Ferraro said it's not clear what became of the gator.

"We don't know if it's alive or dead or injured."