That's when the terror set in.
"I think she thought she was going for a good swim and then got confused about where to go," she tells The Dodo. "She couldn't really differentiate between what shore to come back to."
Indeed, Nellie, who was about 1,000 feet from shore, was swimming in slow, confused circles. Her horrified owner could only stand on the shore, helplessly.
"I'm not very big and certainly I knew I wasn't strong enough to swim 300 meters [1,000 feet] in each direction and get her back. There was nothing I really could have done."