"She is not unhealthy, she is just really fit and it's quite bizarre that people are saying she is unhealthy," Joshua Milton said.

"I don't think she had a fat bottom; I know everyone on TV is saying that but no, I don't think she did."

Mr Milton, the director of Wollongong's Vision Personal Training Studio, said Demelza arrived at the studio with her mother in April and had since undertaken an individually tailored nutrition and training program with one-on-one fitness expert Ty Johnson.

Five days a week for the past two months, Demelza, 16, has engaged in an hour of weights, boxing, running, rowing, cycling, treadmill and cross-training.

"She has got a great opportunity and she wanted to get down to a certain size to actually follow a career that she has always dreamt of," Mr Milton said.

"It was not extreme - 70 per cent of what we do is through nutrition and 30 per cent through exercise, so she has toned up and she has obviously lost weight through her hips and everything, but realistically she has got a lot more strength through the body."

Mr Milton revealed Demelza squeezed the one hour of training in whenever she could.

"She is obviously a very busy lady," he said. "She came back from the show and went back to school, so she had a fair bit to juggle with interviews and everything, so she would come before school, after school, weekends."

Demelza will face the public vote for the queen of the catwalk title against Sydney's Alex Girdwood, 21, at a live final staged at Luna Park on Tuesday. It will be aired on pay-TV's Fox8.