What Chisaki needs to do is not to forget her unrequited love, but to stop nurturing these feelings/letting them grow. Reminiscing about how she fell in love with Hikari easily leads to the impression that she's actively indulging in her memories, which is frustrating from a storytelling point of view. On the other hand, the sentence "I still do like Hikari after all" was immediately followed by "And so [...] our time [...] finally started moving", so the optimist in me hopes that this is not the message the directors wanted to tell us. Which is why I'll use my imagination to come up with a different interpretation
When she was 14, Chisaki refused to accept her feelings because she was afraid of changing the group dynamic. Her fear manoeuvred her into a corner where she wasn't able to face her feelings directly (even her confession in episode 12 was a half-lie). She never gave herself the chance to move on from Hikari naturally and when she told herself to "grow up"/"give up", it was not because she wanted to move on per se, but because she was forced to do so in order to maintain the status quo. Five years later, she repeats the same thing and is depressed that her 19-years-old self doesn't fit into the group anymore. Again, she fails to decouple her change issues from her feelings for Hikari. Her wariness of change and her love for Hikari were always mutually exclusive.
Episode 19 however seems to be the first time she's completely honest and open about both change and her feelings. She is 19, Hikari's 14...but she likes him anyway. For the first time, the change issue takes a back-seat. The optimist in me wants to believe that the Chisaki we see now is finally able to move on - not because her change issues dictate her to do so, but because she herself chooses to.