Ilyss needs Dannep in order to carry out her plan and rid herself of her weakness.
Dannep was only a means, an object she could use to satisfy her desires for revenge while she became an invincible person.
She didn't care about Dannep, she didn't care what she felt or what went through her mind, Ilyss only cared about manipulating her and using her for her own games, this is Dannep's only reason in her life, nothing more.
"What did you just call me, bitch?" But if that was the case, why was Ilyss angry?
It wasn't the first time Seraphin insulted her or referred to her in a derogatory way, they were best friends, it was common between them.
So what was bothering Ilyss? She herself knew, but she didn't want to admit it.
After having that deeper contact with Dannep, she felt slightly attracted to her, although her attraction is in a twisted way, Ilyss feels a deep ecstasy with Dannep since she hates her, and wants to kill her for being the daughter of those people.
