The thing with the Prisoner is she knows so much about the situation she is in. She might be one vessel that knows the most about her situation.
To get to her route she sees you trust her enough to free her, gets her arm cut off and survives, watches you battle an outside force to not kill her, then is promptly brought back to where she started and you come back.
She has all the information she needs to understand death and injury don't work the same here, you are willing to help her, and there is an outside force who wants her dead and is willing to take over your body to do so.
Why does she tackle you to the ground when you sit too close? Because she can't risk you getting near her with a knife after what happened last time.
She tries to keep up playing the game that nothing happened, hoping you also have noticed something is wrong.
And then her plan. Her perfect plan. She knows the only way out is through you, but last time you have your body taken over for trying to take her out alive. So what if you don't take her out alive. So she places everything on her hope that you have figured out that death doesn't work the same in this place. And she cuts off her own head. Now the narrator has no reason to stop you from leaving with her.