"Maybe she is—" Daniel shrugged. "That's her problem, not mine."
While the two of them were busy with each other, Katherine was burning with jealousy.
When she noticed Daniel was gone, she started looking for him and ended up in the hallway just to find Emma in Daniel's arms.
When her grandmother told her Daniel might ask her to accompany him to the Gala, she was very excited. Attending an event with him would have socially solidified her relationship with him.
Everyone in her social circle assumed they were attending the event together, and Katherine did not correct them.
She impatiently waited for him to ask her, but he never did, making her angry.
She knew Daniel hadn't asked Emma as she was attending the event with Owen. She assumed he would attend the Gala all alone like he always did.
Katherine wanted to be close to Daniel during the event and maybe after. This desperation forced her to accept whoever asked her first to be their partner for the event.
