Foxes, like minks and other plush animals have been bred for their fur for over a hundred years. Juniper and foxes like Juniper are considered "domestic fur-bearing animals". Being that she is descended from animals that were originally bred for their fur means that she has lost many of her natural instincts. These traits were unintentionally bred out of these animals. In fact, "tame foxes" have well over 4,000 genetic differences compared to wild foxes. They were bred to have more of a plush coat, they're bred to be larger in body size. So with being larger foxes and plusher coat - they have a bigger skeleton proportion compared to wild fox. Their coat has straight follicles, while wild foxes have somewhat of a coarse coat and broken follicles. As well as a more friendly temperament. These animals though originally bred for fur, began to also become pets due to their dog like behaviors.
While tameness was not the original intention when breeding these animals, after several generations of relying solely upon humans, their dispositions also began to change from that of their wild counterparts. They became more docile, less shy, and acceptant of human interaction.
Unfortunately, due to those reasons these animals are considered "non-releasable". Their dependence and lack of fear makes them unsuitable to live in the wild. For animals like Juniper, their options are pelt or pet.
And so became the domestic fox.