"I thought some of it was really good. But I thought: 'For freaking hell's sake, she should have stayed under there.'
"It would be more real, wouldn't it? It would be better. I didn't have the nerve at the time. What if Ada just went down, she went down with her piano - that's it," she told the Radio Times.
But Hunter said she was glad Campion didn't change the film's conclusion.
"That was something Jane toyed with when we shot the movie, to end it there. And she's still thinking about it.
"Me, I love that it's a reverie for Ada, not a nightmare or something that haunts her. It soothes her."
The film also won the Palme d'Or Best Film Award at Cannes Film Festival and Hunter took the Oscar for best actress.
New Zealand actor Anna Paquin, who played her daughter, won an Academy Award for best supporting actress.
Watch excerpts of The Piano courtesy of NZ On Screen:
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