You might be talking about the short stories that come with the Touhou original sound tracks. In Changeability of Strange Dream, Maribel Hearn, a modern day university student, visits Gensokyo as we know it in her dreams. She never gets "transported" there, she subconsciously entered herself, and it was only a brief visit. She did apparently manage to bring home some souvenirs, though. You can reach a translated version of all the short stories from the main page.
Arguably, Mountain of Faith, and to a slightly lesser degree Undefined Fantastic Object and Touhou Hisoutensoku, are at least partially about a modern human girl who came to Gensokyo - namely, Sanae.