The dolphin keeper just lied.
Dolphins are not, and have never been, "natural caregivers" and having worked with them for so many years she was fully aware of this fact.
All the rules people are given before swimming with dolphins are for the human's safety, not the animals. Injuries to people working or swimming with them aren't uncommon and training them is a dangerous profession. There's even a film, Blackfish, about how deadly dolphins are.
They're also smart enough to have worked out that any help they give to humans is repaid in food. Meaning they have ulterior motives for their apparent care, an act that takes no effort on their part.
The Keeper was simply perpetuating the myth about dolphins as cute defenders of humans, whereas their behaviour is actually like any other predatory mammal. They're far more like a pride of lions than the agency of nannies people like to imagine.