My Mom has had a loss of what happened to her. Any advice?

Three years ago she had a mysterious episode she fainted then she got up opened the gate to my aunt and to this date does not remember why? Drs. have done MRI and C-scan and nothing is detected, but she forgets the some of smallest details, not like getting lost, or putting he keys in the refrigerator but I tell her something and she immed. forgets, I need help on who should she see, something is gong on with her!