I wonder if what Mika said will come back later, e.g., in a way of saying that her "fiction yuri" was the idealized version, which Watanabe was actually looking for at first with her obsession, while "real yuri" can take many unexpected shapes, which may seem imperfect, like her relationship with Yoshioka.
But regardless, the way she put it sure hit Watanabe hard and badly. I'm glad the poor girl recovered. And in the end, she already knew the answer.