"You can't sit at home and do nothing".
She's the oldest volunteer on Tiritiri Matangi and 78 years older than the youngest, a 13-year-old high school student.
Rothwell said it didn't take too much effort to get two ferries the island, and she had rest days in between.
"I just walk down the road to Bayswater Marina and get on the ferry to town, then I pick the Tiri boat up at 9am."
She liked to sit on the ferry's top deck for a dose of fresh air.
It was the people that made Tiritiri Matangi special, as no matter the weather you would never hear anyone complain, Rothwell said.
"They can come off the boat on a rough day, wet through, with sick bags all over the place, and they still won't complain, it's not like an ordinary tourist place."
The island was always in need of volunteers, Rothwell said.
"You've got to keep working at it because the younger ones move on to different jobs, and the older ones keep dying which is a bit of a shame."
Rothwell no longer stayed overnight to volunteer, as she preferred the comfort of her own bed.
"I like to get home now, but it's good when you stay overnight because when you do you'll see a little blue penguin wandering around and kiwi and morepork.
"The kiwis are very hard to see, but they make a hell of a noise."
Rothwell, originally from the UK, said a passion for birdlife was sparked by her father, who would watch blackbirds and thrushes nesting in a hedge near their home and always knew when they'd hatch.
Her own grandchildren and great-grandchildren also shared an interest in nature, but they were "all living in Australia unfortunately", she said.
Rothwell encouraged Aucklanders to get out to Tiri.
"Of course age doesn't matter [to volunteer], as long as they're fit and can walk they can do it."
Tiritiri Matangi shop and guiding manager Mary-Ann Rowland said the island had about 300 volunteers, whose jobs ranged from planting and infrastructure maintenance to guiding and bird monitoring.
"What's happened is we had plenty of guides, then we just got more and more popular. Now just about everyone who comes out wants a guided walk because the guides get so much praise on Tripadvisor."
Rowland said they weren't losing guides, they were "absolutely keeping them", but they needed more to volunteer due to growing demand for their walks.
"Volunteering is all about giving, and I think it's through giving you get the most amount of happiness you can."
Tiritiri Matangi
• The name Tiritiri Matangi means "a place tossed by the wind".
• The island sits off the tip of the Whangaparaoa Peninsula and takes about 75 minutes to get to from Auckland.
• DoC manages Tiritiri Matangi as a scientific reserve, protecting the island for its wildlife, conservation, scientific, recreational and historical values.
• The island is host to little spotted kiwi, bellbirds, moreporks and kokako.
