Sleeping on it, I think the problem is a confluence of a few things:
1. Lillian stole her fiancé and turned the whole kingdom against her, effectively disgracing and exiling her. Without Ciel stepping in, Evie'd be up shit creek.
2. But wait, it turns out Lillian was her friend, so it was also a deep betrayal, too!
3. Oh, but she was doing it for Evie's sake... somehow?
4. Anyway, Ciel needs to do something big to prove herse- oh, maybe not.
5. Look, she's clearly in lesbians with Evie, but also still committed to the shitty Prince and won't be hanging around as a constant presence? What?
So a love-rival-who-isn't came-only-temporarily to end-but-not-really her friend-but-acually-crush-but-actually-actually-neither-because-betrayal's relationship.
It's hard to make it hang together, especially since it's only chapter 3 and plenty of other interesting threads have been left dangling in the wind.