Channing Day, a 25-year-old medic with 3 Medical Regiment, died from injuries sustained while on patrol in the Nahr-e Saraj district of Helmand Province on Wednesday.
Corporal David O'Connor, aged 27 and from 40 Commando Royal Marines, was also killed in the incident involving a suspected Afghan insurgent.
Corporal Day's parents Leslie and Rosemary, sisters Lauren and Laken and brother Aaron said she was a "fabulous daughter, sister, granddaughter, cousin, niece and friend".
They continued: "Channing was bubbly, sporty, beautiful and lived her life for the Army."
She has died doing what she lived for and in the life that she loved.
Family of Corporal Day
"She will be remembered by all who knew her as a wonderful girl who never stopped smiling and who had an infectious laugh.
"Channing played football for Northern Ireland as well as ice hockey and also gained her qualification as a ski instructor through the Army.
"She was also the Northern Ireland Gymnastics Pairs Champion. A girl who lived her life to the full without ever giving up on her dreams. She will be so sadly missed by all."
Channing Amanda Day was born in Swindon, Wiltshire and grew up in Newtownards.
She joined the Army in 2005 and was deployed to Afghanistan on 2 October as a Combat Medical Technician Class One with the United Kingdom Medical Group.
She was based at Patrol Base One in the Nahr-e Saraj District of Helmand Province, where she provided medical support to 40 Commando Royal Marines.
Lieutenant Colonel Phillip de Rouffignac, Commanding Officer of her regiment, said Corporal Day was looked up to as a veteran of previous Iraq and Afghanistan deployments, and said she had a mature voice of experience and gave good advice.
He continued: "Corporal Channing Day was a star for the future.
"Although only 25, she had recently been promoted to Corporal, and her current operational experience in Iraq and Afghanistan made her a natural choice for the demanding role she was undertaking in support of 40 Commando Royal Marines.
"Diligent in every respect of her preparation, she had worked hard all the way through the build-up training and led by example in all that she did.
"Hugely popular with her friends in Preston, Catterick and in Afghanistan, Corporal Channing Day made the most of everything and had lived a lifetime in a short time. An Army footballer, she was a real team player in every sense. Corporal Day will be sorely missed, and the thoughts of all our Regiment are with her family and friends at this difficult time."
Before joining the army, Channing was a pupil at Strangford Integrated College.
Acting Principal Paul Maxwell said she came from a very popular family and described her as "an amazing sportswoman".
"But, right from when she came to the school and was talking in careers lessons, the army was her career path. That was what she really wanted to do and wanted to follow through and was obviously successful in that," he explained.
He described her as "very bright", "very bubbly" and "extremely popular" adding: "The school is deeply shocked by the news and extend our deepest sympathy to the whole family. She was one of those pupils that everyone had a good word for."
First Minister Peter Robinson said: "It is with great regret and sadness that I have learned of the death of this young soldier who has tragically lost her life while trying to protect and save the lives of those around her.
Our thoughts and prayers are with her family, friends and colleagues who continue to give service to their country.
"The incredible bravery displayed by our armed forces is immense and the risk they take on a daily basis can never be underestimated."
Mike Nesbitt, leader of the UUP, described the death as "just dreadful".
"I don't think anything actually prepares you for the phone call or the knock on the door or the switching on of the radio to hear the news and wonder, 'Is that my friend, is that my dear one who has gone?'" said the Strangford MLA.
Local DUP MLA Jonathan Bell said his sympathy is with the Day family.
"I would extend our heartfelt sympathy to the family of this heroic 25-year-old girl, who I understand comes from Comber, in my own constituency in Strangford.
"Our thoughts and prayers are with her family, her loved ones, and also with the soldier from the 40 Commando Unit of the Marines.
Major Laurence Roche, spokesman for Task Force Helmand, said that he was "extremely sorry" to announce the deaths.
"This is dreadful news for all of us serving in Afghanistan. Our sincere condolences go to their families, friends and colleagues at this time of grief."
It is understood the Taliban has claimed the incident as a "green on blue" attack by a member of the Afghan Uniformed police. But the MoD said the Afghan man was not on patrol with British troops.
An MoD spokesman said: "On October 24, during a UK foot patrol in the Nahr-e Saraj district of Helmand Province, there was an exchange of gunfire that resulted in the deaths of a Royal Marine from 40 Commando Royal Marines, a female soldier from 3 Medical Regiment and an Afghan man who is believed to be a member of the Afghan Uniformed Police but who was not wearing uniform at the time."
The spokesman said an investigation is ongoing into what initiated the exchange of gunfire but the situation "remains unclear".
Channing was on her last tour of duty in the country. She is only the third British female personnel to have lost her life in Afghanistan since the conflict began in 2001.