I think she should definitely go see her doctor right away. In fact, if she is blacking out this is an emergency situation. Pain and headaches can be caused my menstrual issues. But, the blackouts are not normal and need immediate attention. I am assuming the blackouts are not in relation to alcohol use. There is just no way to know without running some tests. Please take her to the doctor right away!
I'm facing the same problem. I always have sharp pains and headaches. Endometriosis can cause severe headaches and pain esp in the lower abdomen. I took evening primrose oil and feel a bit relief. Late period might due to stress and hormonal changes.