Whether your power of attorney is still effective depends on whether your mother revoked it. If she did not, though it sounds like she did, then both you and your nephew have valid powers of attorney and can act for your mother. If your mother revoked your power of attorney, then your nephew is in his legal rights to act for her, assuming that your mother knew what she was doing when she gave him a new power of attorney. Since you suspect that your mother was not competent and is not being well taken care of now, your first step in reporting the case to the Office of Aging was totally appropriate. If this was not effective, your only alternative may be to seek guardianship over your mother. This would bring the matter to a head in your local probate court and, most likely, result in the appointment of an independent, non-family member as guardian for your mother. These types of cases can be extremely acrimonious, time-consuming and expensive, but it may be the only alternative.