In recent months Turkey has shifted its focus from fighting Isis in Syria to preventing the YPG from establishing a foothold along its border, arguing that the YPG is linked to its own insurgent group, the Kurdistan Workers party (PKK). The US, EU and Britain, however, do not consider the YPG a terrorist group, which it has supported in its fight against Isis since 2014.
Dirk Campbell said his daughter had dedicated her life to the fight against unjust power and privilege.
He said she was a committed human rights and environmental campaigner who would put herself on the line for what she believed in.
It seems a small thing, but I remember when she was 11, she protected a bumblebee from being tormented by other kids at school, he recalled. She did it with such strength of will that they ridiculed her. But she didnt care. She was absolutely single-minded when it came to what she believed in, and she believed what Turkey is doing is wrong.
He said his daughters passion for campaigning was inspired by her mother, Adrienne, who was well-known on the south of Englands activism scene and died of breast cancer five years ago. Anna was a credit to her mum, my wife, and was carrying on a lot of the kind of work that she was doing, he added.
Campbell told her father of her plans to travel to northern Syria last May after she heard about the grassroots feminist and socialist revolution that has swept Rojava (the semi-autonomous Kurdish region of northern Syria and heartland of the YPG/J) and inspired the Kurds fight against Isis.
I didnt try to stop her, Mr Campbell said. Because I knew, once she had decided to do something, she was unstoppable. Thats why she went to Rojava: to help build a world of equality and democracy where everyone has a right to representation. When she told me she was going I joked: Its been nice knowing you. I just knew it might be the last time Id see her.
Upon arrival in Rojava, Campbell completed the YPJs mandatory month-long military training course, in which new recruits learn basic Kurdish, weaponry and battlefield tactics on top of a crash course in the egalitarianand feminist ideology of the YPG/J, and was assigned to an infantry division, comprising a mix of Kurdish and international fighters. There she was given the nom-de-guerre Heln Qerecox and sent to the front.
YPJ sources said she spent her first months in the country fighting in Deir ez-Zor, Isiss last major stronghold and scene of the jihadist groups bitter last stand. But with Isis now on the brink of defeat, foreign fighters within Kurdish ranks have faced a choice: return home or remain in Syria to help the YPG repel Turkeys attack.
After the initial attacks on Afrin, comrade Heln insisted on joining the operation to defend Afrin, said Abdullah. Before leaving, she had already received her military training, and, although we wanted to protect her and did not agree with her decision she incessantly insisted on her wish to leave for Afrin. She even gave us a condition: Either I will go home and abandon the life as a revolutionary or you send me to Afrin. But I would never leave the revolution, so I will go to Afrin.
She added: For us, as the YPJ, comrade Heln will always be a symbol as a pioneering internationalist woman. We will live up to her hope and beliefs. We will forever pursue her aim to struggle for women, for oppressed communities.
Mark Campbell, activist and co-chair of the Kurdistan Solidarity Campaign, added: Anna, by all accounts, was taken deep into the heart of the Kurdish people as she stood side by side with them in their darkest hour. Our thoughts and condolences are with Annas family and friends as this time.
Campbell is believed to be the eighth British citizen killed while serving with Kurdish forces in Syria.