I scrolled through the comments for a bit and im pretty sure you need to progress some of the other girls before you can do this one. it's left me quite confused as well. If i discover what quest it is to progress i'll drop another comment
Most recent event was that mikasa told me to come to her tent at night. if you sit around the campfire after that chat it should allow the event to play.
the key characters required to progress get to this point were: Sasha, Annie & Mina. they unlock a lot of progression for other characters.
