It was Fenrir and Anthony Goldstein who had been behind the attacks. She suspected it, but he likely orchestrated the attacks with Goldstein and whoever this Ivanova is. Hermione feels a flash of hurt and annoyance that he hadn’t shared this with her. She told him she would help him, that she would do anything. It feels almost like a betrayal, especially when she knows she could have prevented him from being locked in the Lestrange manor. 