Noticing a rip just metres away, the Napier Girls' High School student swam across to the group and asked if she could help them to the shore to check that they were okay.
"I didn't actually notice until I got to the shore that their mum was standing right on the beach watching them. I brought them in and she said she was just about to jump in with her clothes on; she was that worried."
Waimarama Surf Lifesaving Club chairman Tony Pattison, who was on the beach at the time of the rescue, said the situation could have been much worse if it weren't for Ms Herbison's efforts.
"It was being at the right spot at the right time and, to Bella's credit, being vigilant and knowing that there was a problem about to occur which is her lifeguarding skill.
"It just highlights that parents with kids need to be constantly watching the kids and reminding them not to go too far out. It was just really good that Bella was there and did a fantastic job."
Ms Herbison said she had been a lifesaver for two and a half years and, aside from practice rescues, this was her first real experience in the water.
"In the situation I was able to take action instead of just standing there and watching them struggle. I felt pretty proud and was surprised someone has noticed other than the mum."
She said she planned on being a lifeguard at the Waimarama Surf Life Saving Club for the rest of her life, describing the club as "a family".
"I'm just thankful to the people that taught me to be the lifeguard that I am now and all of the opportunities I've had to build me to cope with these situations, even when I'm not on patrol."
Mr Pattison said it was important those swimming on beaches this summer swam between the flags while patrols were in force, never swum alone and kept to waist-deep water if they weren't confident swimmers.