If she has a Will, then that document says who gets her "household belongings," even though she did not make a specific gift of a particular item. The will should state who receives the rest and residue of her estate and that is who gets the household items. Your POA must be "durable" or it is invalid at the moment your sister became incapacitated. If it is a durable POA, you do not have the authority to decide who gets these items of her property.
