For a brief moment, it was confusion that took over Frigga's gentle features. That was hardly where she'd intended this to go. But she knew, now, that this was no trick. At least, not on someone else's part. That demeanor, the defensive nature... That was definitely, without question, her youngest son. He was still so angry. So hurt. And despite her own hurt towards him, every maternal instinct in her longed to hold him and comfort him. To tell him the monsters in the stories Odin fed the boys weren't real, that he and Thor were protected and she'd care for them both.
Only so many of those monsters were real, and Loki had seen his share of them. Found out a part of him even was one. And there was nothing she could do to shield him.
Her face finally fell, settling into something resembling remorse. He thought he'd been trapped just as much as she'd feared. To not be biologically hers, he was too much like her for his own good sometimes. She knew, even then, even as his anger was slowly unleashed, that even if he tore himself from her for good, she'd never stop considering herself his mother. "My boy..." she said softly, wanting to reach for him but forcing herself to move at his pace. "How hurt you've been... Who's tricked you so?"
Her tone was low, gentle. No longer teasing, no longer afraid. She had to hold on to the belief that if anyone could reach the troubled young god, it was her. For centuries she'd shown him a mother's love. It had to have meant something.
She was also skilled enough with her own magic and knew his enough to know what he'd just done. She had, after all, guided him on how to do so. How it was no longer the physical presence of her son that stood before her. She stepped out from the shadows, dissolving her own projection in his view. "You can come out now, my darling. I promise you...this is no trap. There is nothing to be sprung."