"His dream was to see me graduate."
Johnson contacted two of her lecturers, Joce Stewart and Judy Searle.
"They commented on what a wonderful idea it was, so they ran it past the head of nursing."
Orginially it was going to take place at EIT, but by the time the day rolled around, it was clear Chapman was not going to be able to go into the polytechnic.
"I got on the phone to my lectures and said, granddad is not going to be able to come it, we're not going to be able to do this, I'm devastated."
So the lecturers decided to take the graduation to Brooke and her granddad.
They brought a copy of her transcript, which showed all her achievements over the last two years, and a graduation robe to her house.
Her granddad was semi-conscious during the graduation, and managed to say a few words about Johnson and her cousin, Luke Chapman, who is also studying at EIT.
Her mother, uncle and son Cruz also attended.
"It was very emotional, because obviously it's a bittersweet feeling."
Chapman passed away on January 29, only five days after the mock graduation was held.
EIT's head of nursing Clare Buckley said it was important for them to support Johnson and her granddad.
"We just thought it would be really neat to have a little graduation service. Obviously she couldn't graduate, but it was acknowledging her success in the programme to date.
"We just thought, it wasn't difficult to organise, it was just lovely."
She said nursing can be a stressful degree to complete, and it was important to acknowledge those who support their students.
"It was a way of being able to acknowledge whanau."
Johnson said she was very grateful to EIT.
"They didn't have to do what they did, but they did, and they helped my granddad's wish come true."
When Johnson officially graduates she will wear her grandfather's watch, so he is with her on the day.