Perhaps Miko would mistake Rin Satsuki for a fallen celestial at first. After, of course, lending her aid from her fall, she would likely learn the truth soon enough of her true specie, but I'd imagine they'd still end up getting along famously with each other due to Miko's nature as a Saint and Rin's nature as a Kirin.
What if ZUN had included Myouren as the final boss instead of Byakuren as he originally had planned to in Touhou 12 Undefined Fantastic Object?