TBH, I don't know why the "girl's love" tag is even applied to this manga because I haven't really seen any actual romantic developments between the protagonists. Maybe it happens in the future, but so far it hasn't really given off that impression as this manga is more along the lines of the usual CGDCT material. The only "yuri" in this manga so far is between literal swords with no human form.
And it's simplest terms girls love or shojo ai is just relationships between girls doesn't necessarily need to be romantic in nature. However, there are what I would personally define as soft core girls love manga out there were the premise is basically sisterly love. If that being said, I'd argue that there's been a handful of Yuri moments in this series. You have the amount of times Charlotte has said. The other girls are seducing her. You have the fact that Laura loves being hugged while going to sleep by Charlotte.
Not all things start off romantic at the beginning. Just look at a series like akebis sailor uniform It seemed fairly friendship oriented in the building, but now it's a decent amount of romance in there.