Do you think it's possible it happened after Ida's death ? Maybe she died because of Rocks's involvement with him and Harald crashed out. I think this might be the thing that pushes him to face Rocks again and also remove his horns because of shame since he didn't kill Rocks when he had the chance.
Loki still idolizes Rocks. He may be cruel, but Ida was one of the few people who showed him kindness. I don’t think Rocks killed her.