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A do-or-die attitude has resulted in the 16-year-old going from strength to strength on the Otago tennis circuit, all while balancing schoolwork and other sporting commitments.
The left-hander's biggest break in tennis to date was winning the Otago Open in March, at just 15.
She beat Jessie Stevenson in the women's final 6-1, 2-6, 6-3.
Tennis is a family affair for Dellaway, who started playing aged 10, hitting with parents Kevin and Jo, and older brother Cameron.
''My whole family plays, so I just got dragged along to the courts,'' she said.
She was 12 before she entered her first tournament, but proved to be a natural, and it was not long before she started beating the boys in North Otago.
A big influence on her tennis was Janos Manyai, a highly-ranked Hungarian player with whom she trained during the 2012-13 season.
In the winter, she is also a force to be reckoned with in the midcourt for the Waitaki Girls' High School senior A netball team, as well as proving herself in cross-country, touch and athletics, but tennis remains her major focus.
After school, she can be found most nights hitting with her father at her local courts in Papakaio.
''We try and get down there as quick as we can and we'll go until dark when we can't see the ball,'' she said.
Dellaway trains with Steve Dries once or twice a month, but much of her guidance comes from her father.
Her long-term goal is to secure a scholarship to play college tennis in the United States.
Depending on where that could take her, she would like to play in Auckland's premier league.
She entered her first ITF tournaments this year and gained ''great experience''.
A broken wrist could have put her out of action for up to six weeks over summer, but arm in cast, Dellaway continued to play interclub in North Otago using her right hand.
While not at full strength after the injury, she still made it to the New Zealand junior championships, drawing 14th seed Diana Deyeva in the first round.
Dellaway fought hard, but lost to the Aucklander in three sets 6-1, 1-6, 7-5.
She went on to prove herself in the consolation round, winning two of her three matches.
Being based in North Otago could be tough, but she said it was all about making the most of her opportunities.
''It's good that we can play the men, but it's sometimes hard not playing girls my own age,'' she said.
''There's a lot of travelling involved and the grass courts are quite hard to play on.''
For Dellaway, the attraction of tennis is the pressure.
''Team sports are good, but with tennis, you know why you're losing and it's all on you to turn it around. I just enjoy it,'' she said.
Name: Rebecca Dellaway (16).
School: Waitaki Girls' High School
Achievements: 2014 Otago Open winner, ranked No 1 in North Otago, Southern under-16 representative.