she dosent take over your body in at the end of the game, more the obbosite, the fanon story says that she controlls you and is the reason for the genocide route, and after frisk kills flowey, all the determination is enough to wake chara up from death, wich makes her no longer control frisk, she just destroys the world ( aka the game ) after that, she dosent take over you, while you can sell your soul to them, that dosent mean she starts to controll you