@Tearsax
There's a lot to unpack into why concluding she's a lesbian from this would be a bit of a leap.
It was an overly comical reaction because she wasn't expecting a text message from them. Exaggeration is common in manga, and many other forms of art.
Plus Kuroki has been established to be a bit of a recluse and an introvert, as some of the other characters not close to her comment how she seems scary and she has some strange hobbies like fortune-telling. Plus, when you consider the fact she's looked down upon because of how blunt she is...Yeah, getting a sudden text message in the middle of the night and having that reaction is understandable.
Also it was established both of the other girls are into Shun, which Kuroki is aware of, so I don't think that will lead to any Yuri action, especially because it has not even been hinted at that Kuroki is anything more than a friend/mentor to the other women of the office, nor that she has any feelings for women. It would just come out of nowhere