Damiana Humphrey, 19, said the incident happened while she was on vacation with her family.
Humphrey said she was splashing around in the water when she felt teeth in her hand.
Her brother screamed, "Shark!" Her parents rushed into the water to help her.
"I thought at the time, I lost my hand or something. Then, when I saw dad, that's when I finally saw my hand. And that's when I started freaking out, basically," Humphrey said.
Humphrey says four tendons in her left hand were severed, and her hand is now in a cast.
In Galveston County, there have only been 19 unprovoked attacks since 1911, according to the International Shark Attack file.