In theory, Saira isn't vulnerable to other people's magic. She has enchanted jewelry that keeps it from taking effect on her person.
She's well aware of how little assurance this is. It won't stop someone from freezing the air around her head to suffocate her. It won't stop someone from telekinetically throwing something heavy at her.
Also, she was not previously aware, it will not stop a snake's mysterious mirror mouth from being a portal to another universe. Well, she wouldn't have been better off in its stomach, now, would she.