Dr Karen Woo was among nine foreign aid workers who were shot dead on Friday in a remote part of the country.
The Taliban claimed responsibility, accusing the victims of being spies and Christian missionaries.
The 36-year-old was engaged to Mark 'Paddy' Smith, a former soldier from Newtownards.
The couple had met in Kabul and were due to marry in London at the end of the month.
In a statement, her relatives said: "Her motivation was purely humanitarian. She was a Humanist and had no religious or political agenda."
They continued: "She wanted the world to know there was more than a war going on in Afghanistan, that people were not getting their basic needs met.
"She wanted the ordinary people of Afghanistan, especially the women and children, to be be able to receive healthcare.
Speaking on Sunday, Paddy Smith said: "She was an extraordinary person. You don't find too many people like Karen Woo in this world unfortunately.
"She was a gregarious, loving, caring person.
"I will miss her love for life. Anybody that met her could not help but smile. She just made people happy.
"She would help people wherever she could, she always had time for people. She was someone you could rely on - she would never let you down."
The family of Dr Woo, called her a "true hero".
"She undertook this trek as a medical doctor, accompanying medical supplies and to provide treatment to people who lived in an extremely remote region who had little to no healthcare available.
"Her commitment was to make whatever difference she could. She was a true hero. Whilst scared, she never let that prevent her from doing things she had to do."
Dr Woo's family said they were "so proud" of everything she had achieved.
The statement continued: "Karen, you were an inspiration to everyone you met. You combined brains and beauty, intelligence, drive and kookiness in equal measure.
"You led an intensely packed and rich life: dancer, model, stunt plane walker, doctor and aid worker. Whatever you set your mind on, you did so with passion.
"You were the embodiment of seizing the moment. You went through life always believing the best of everyone despite everything you've seen.
"I hope that the legacy you leave is to inspire others to give love and aid rather than perpetuate hate and violence."