I heard Fl can't kill that bitch cause system forbids it

I thought the system doesn’t talk to FL???But I have a question cause I get a bit confused on how it’s worded but where did you hear it say it’s not aloud for the girl to die? I mean the princess doesn’t kill her but she can, can’t she? She could’ve killed the so called Mc by now cause she’s the princess and what prevents her from doing so is it the system or does she the princess need something from her.