well, I personally came up with this translation :
"Over on Gensokyo, the land which values isolation, forget their interests in others to devote themselves to self-study is the path of the hermit, but the evidence is irrefutable that she was working hand to hand with the outsider."
However, I found that someone already translated this book that way :
"Here in our isolation-revering land of Gensokyo, this hermit-- one who walks the road of self-improvement while forgoing concern for others-- is clearly conspiring with an outsider, and this photo is unshakable proof!"
They took more liberty and the translation is not literal but it still helped me understanding the meaning of this phrase.
Source