So in the end who's her yuri?
The LN industry is killing storytelling. They don't know if they'll ever get a second volume so they either reveal and resolve everything in the first volume leaving no plot open for future volumes or they won't resolve anything but then don't get any other volume so the story remains incomplete. Axed manga at least have a second volume to end the story.
I hope in some kind of twist like the MC wrote the letter herself (but it doesn't seem to be the case) so she could have dates with all the three girls and not just revealing that it's one of the three.
Sakuhi is a great character, she deserved to be more developed but boring stuff like exams and elections stole away too much time.