Ilia is a member of the White Fang.
Through the White Fang, Ilia is brethren with the two fox Faunus. They know her well enough to be aware that she has a history with Blake Belladonna and to inform her of Blake's return.
Blake's return to Menagerie is mentioned by the Albains as something that would be of significance to Ilia. During their altercation, while Blake is still unaware of her identity, Ilia does not attempt any direct or harmful attacks on her. When they see each other Ilia appears to be saddened and tells Blake that she should not have come back. Judging by their interaction, it implies that they used to be close.
The two first meet with an immediate confrontation, due to her being caught spying on him and Blake. In "Two Steps Forward, Two Steps Back", she wounds and renders Sun unconscious with her whip to prevent him and Blake from chasing her.