Northern Ireland soldier Channing Day, who was killed in Afghanistan, had dreamed of joining the Army since she was a schoolgirl, a teacher at her former school said.
Corporal Day, who served with the 3 Medical Regiment, died alongside Corporal David O'Connor, of 40 Commando, after being injured on patrol with C Company in the Nahr-e Saraj district of Helmand province on Wednesday, the Ministry of Defence said.
The pair were overseeing the training of Afghan Local Police when their patrol came under fire near the village of Char Kutsa.
Royal Marine Cpl O'Connor, 27, and medic Cpl Day, 25, were fatally injured during the firefight, the MoD said.
Cpl Day grew up in Newtownards, County Down before joining the Army in 2005.
In a statement her family said: " 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.
"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 was a fabulous daughter, sister, granddaughter, cousin, niece and friend. She will be so sadly missed by all."
Paul Maxwell, acting principal at her old school, Strangford College, said she had excelled at gymnastics, trampolining and netball, and achieved top grades in PE.
Mr Maxwell said: "It was not just that she was good but that she always showed commitment, she stayed after school and did all the practice.
" She always said she wanted to join the Army, she was pretty much focused on wanting to join the Army."
He added: "Every pupil is dear to us and I can remember Channing as if it was yesterday, somebody we remember as being young, and still so young, is suddenly killed in such a tragic way."
Cpl Day was deployed to Afghanistan earlier this month as a Combat Medical Technician Class One with the UK Medical Group. She was based at Patrol Base One in the Nahr-e Saraj district, where she provided medical support to 40 Commando Royal Marines.
An MoD spokesman said: "Cpl Day was a popular and well respected member of both 3 Medical Regiment, and Transition Support Unit Nahr-e Saraj. A veteran of previous Iraq and Afghanistan deployments, she was looked up to, especially by more junior soldiers in her Squadron, as a mature voice of experience and good advice.
"Cpl Day clearly displayed the potential to go far within the Army. Her diligence, her loyalty to friends and comrades and the high opinion in which she was held by all ranks made her a natural medical leader.
"Her courage, selflessness and commitment in adversity embodied the ethos of the combat medic, and will be long remembered by all those who had the honour to serve with her."
Lieutenant Colonel Phillip de Rouffignac, Commanding Officer, 3 Medical Regiment said Cpl Day was a "star for the future".
Cpl O'Connor, 27, lived with his mother in Havant, Hampshire.
A statement released by his family said: "David's family and friends are greatly saddened by his loss and hope to be left to grieve privately."
Cpl O'Connor was deployed to Afghanistan at the end of September as a Section Commander as an acting corporal. He served with Charlie Company, 40 Commando Royal Marines as part of Transition Support Unit Nahr-e Saraj, and was based in Patrol Base 1 in the southern part of Nahr-e-Saraj District, Helmand Province.
An MoD spokesman said: "Cpl O'Connor was an outstanding Royal Marines Commando. He displayed true Commando spirit in all that he did and was ferociously dedicated to his men, his Company and the Royal Marines.
"He was an inspirational leader and an excellent soldier; his loss will be felt not just at 40 Commando Royal Marines but throughout the Royal Marines Corps."
Lieutenant Colonel Matt Jackson, Royal Marines, Commanding Officer, 40 Commando Royal Marines said Cpl O'Connor "was one of the best".
He said: "He was loved and respected by those around him and was relentless in the pursuit of excellence in his duties.
"Utterly professional, his four operational tours of Iraq and Afghanistan marked him as one of the most devoted individuals in the Commando."
Secretary of State for Defence Philip Hammond said he was "deeply saddened" by the tragic deaths.
He said: "Both have been highly praised by their colleagues for their courage and strong sense of duty. My thoughts are with their families, loved ones and colleagues in the Royal Marines and 3 Medical Regiment."