No, if your grandmother is mentally competent, than your mother cannot evict you against your grandmother's wishes a person's attorney-in-fact or agent the person given power by a power of attorney or POA cannot override the wishes of that person, so long as that person is mentally competent. If your grandmother does not want you out, you do not have to leave. However, if your grandmother does not want conflict with her daughter and goes along with your mother, then yes, your mother would have the authority to evict you. In order for you to stay, your grandmother needs to be willing to stand up to your mother.