Well my thinking here was that Clara has some knowledge about vampires, or at least the lore of them that she learned from watching a lot of vampire movies and shows with her dad who was apparently a huge fan of vampires while at that time Kyra still couldn't remember any of her vampire past. She only knows the basics as she lived through the time before vampires went extinct in this world. The thing about her dad being a fan of vampires and teaching her is mentioned later on when they have a conversation while shopping for clothes for Kyra.
Besides that, Clara is also incredibly bright, good and caring person, despite all her past hardships in life and she wants to try and keep her positive outlook on life.
However, if you play Clara rejected/spiral path you realize that her lore knowledge doesn't really help her much and she doesn't know how to deal with her vampire state and is becoming increasingly unstable.
Also, Kyra knows how to control her hunger, she was just sleeping for so long that the hunger took over and she lost that control. Call it vampire frenzy. This is where the hunger system comes in, if the player gets too low on their blood, they will lose control. This is what I was trying to show here, but maybe I failed in that. Later when she's all fed up, you realize how much control she actually does have.
On romance path Clara basically grounds her and Kyra does the same for Clara, they help each other keep control. All this happens through their blood bond, it's a mental thing. But if you reject Clara then she doesn't get that same support and Kyra is instead kind of trying to push her and be firm with her as her sire, but as a result of it Clara can't deal with it and starts spiraling out of control. All of this is once again indicated with the Hunger meter where on romance path she loses less blood when performing abilities or doing something that has her gain more hunger, while on rejected and solo paths she loses more. It's all connected together