Alessandro Intini, an on-looker who filmed her, told the BBC: "It was a wall of water which took the girl off her feet."
Chris Ingall, of Brighton and Hove City Council's seafront operations manager said she was "very lucky" as she could have been swept out to sea.
He continued: "If she had been any deeper in, that wave would have come behind her, over the top of her, and pushed her down into deep water.
"Fortunately, the force of the water pushed her back up the beach, otherwise that could have been a very different outcome."
In the Brighton sea, the pebbles slope very steeply and it only takes a few steps to be out of your depth.
The council official warned dog walkers to keep their animals on a lead in these stormy conditions.
He advised that if an animal does get swept out to sea, it is likely it will float and be pushed back to land by the waves.
Ingall said: "In those sorts of conditions you're not going to be able to get to your dog."
He also commented that she looked "shocked and cold" after the rescue attempt.