"It was hard to do because the paintbrush was quite fat but I managed to find a thinner brush. I quite like drawing and painting and my favourite is horses because they are my favourite animals," she said.
Her artwork contains a poignant message: "Do not cut trees down".
Her mum said she had no idea Ayla was working on something that big although her daughter mentioned about her painting.
"I am all for creativity in schools and in classrooms and she comes from a creative family.
"My mum encouraged her," Ms Allan said.
"Every holidays we go to, she draws pictures of her holidays. She drew dolphins she saw in Opononi and when we went to Waiheke, she drew a picture of quite a detailed dinosaur."
She sees Ayla following in the footsteps of her maternal grandmother who taught art in school.
"I was so pleased to hear she had won, although I wasn't really surprised because I thought it was time she won something."
For her effort, Ayla will receive a trophy at an awards' ceremony on Saturday, her artwork will be professionally framed and her school will receive a free workshop from a BACH artist.
The Bach chairwoman Heather Carthew said the judges liked the fact that Ayla took ideas from Hundertwasser's style but came up with her own work.
Full list of winners are:
Year 1 - Winner: Katara Karena, Merit: Troy Clifford, both from Hora Hora School
Year 2 - Winner: Connor Rau, Whau Valley School. Merit: Sky Pihama, Onerahi Primary.
Year 3 - Winner: Ngaia Lovelace, Onerahi Primary. Merit: Nicolace Brown, Whau Valley School
Year 4 - Winner: Ayla Nicklin Onerahi Primary. Merit: Alex Walker, St Frances Xavier.
Year 5 - Winner: Anabella Hugo, St Frances Xavier. Merit: Lorelei Stanley, Onerahi Primary
Year 6 - Winner: Affe Schreuder, Merit: Grace Aukett, both from St Francis Xavier.
Year 7 - Winner: Alice Qin, Huanui College.
Year 8 - Winner: Mia Howe, Huanui College. Merit: Kayla Potter, Kamo Intermediate.
Overall Winner: Ayla Nicklin (from Year 4, Onerahi Primary).