Elizabeth Rose said her sister, Lindsey, suffered injuries so severe that a plastic surgeon had to work on her face, KABB reported.
Lindsey told the television station she and her husband had finished tubing near Devil's Playground and had momentarily set their tubes aside. When four women and a man picked up the tubes, Lindsey told KABB she asked what they were doing.
According to Rose, that's the last thing Lindsey remembered. The people who allegedly attacked Lindsey left the scene, according to her sister.
"She got hit,and she was out," Rose told KABB. "She doesn't remember anything after that.
"I wish I was here; I wish I could have saved her. It's devastating."
Lindsey's husband called Rose, saying his wife had a big gash on her forehead, the television station reported. While the woman will be OK, her family members are upset.
"Yeah, we are angry, because she didn't deserve it. No one does," Rose told KABB.
Campground officials did not comment, the television station reported. The Comal County Sheriff's Department has not responded to a request for comment.