It's not stated which character it is. For all we know, it could be Reimu.
True, but this character holds a twig, also it's leaning back. this makes me think that this girl is based on this illustration posts #103368 Also, the description says "白山修験" the same name as zun006.jpg illustration.
also, Zun never mentions Reimu, unlike other illustrations where he does (example zun000.JPG, zun012.jpg, zun001.JPG or zun004.JPG) Instead, Zun comment only says "shrine maiden" it makes more sense if you read the comment from zun005.JPG (the drawing before this one) which says he wanted to create new characters. I mean, if she really is Reimu, ZUN would have mentioned it just like it did with the other illustrations, whenever Zun drew Reimu he said that she was Reimu.
even so, there is a very remote possibility that maybe and only maybe this girl is Reimu. but considering that at that time, Zun created several new characters (especially shrine maides because it was easy to draw according to their comments) and that whenever he drew Reimu he mentioned him, I think they are more than enough evidence to believe that they are not about the same character and probably she is a totally different shrine maiden.
