She first saw the whale swimming around in circles, apparently distressed, about 6.30pm.
When it became caught on the rocks her partner and his son helped it back into the water.
The whale, which had wounds on its tail and head, started swimming out to sea, but turned and started coming back in, so the men stopped it again.
Ms Butler called the police and officers and firefighters were sent to assist.
She said the whale kept trying to come back in, so they stood around it, stopping it from beaching itself.
An inflatable rescue boat from the Kaka Point Surf Lifesaving Club was eventually used to try to pull the whale to deeper water, but it returned.
Mr Bennett said a decision was made to abandon rescue attempts about 9pm.
A whale would normally be euthanised in that situation, but no-one in the area had the right skills, so it was left to die.
DoC staff would visit the whale early this morning with a scientist from Massey University, who would fly from the North Island to study the whale.