I want to put in my own interpretation on this one shot. I don't think the girl is really worried about them being half sisters affecting their relationship, since she makes that promise with her about going to an amusement park.
I think she felt sad at the fact that her dad never came to see her, even though they seemed to have been living in the same town. Not only that, but he started a life with another family and even raised a daughter who is not that much older than herself.
She had this wishful thinking that her dad cared about her but was never able to come see her due to some complications on his side. So when she realises the truth her expectations are shattered and she is distraugthed.
last edited at May 7, 2020 2:55AM