What Causes Disassociation With Loss Of Memory?

My mother has recently came to live with me .... She now does not seem to recognize me as her daughter.... She has full knowledge and recall of recent as well as long ago facts.... She seems to disassociate me "by name"...from the person she readily knows as "her daughter"...No confrontation with facts or pictures seems to disuade her from this belief... Can you help me with this???