Do we have a viable case to file a suit for medical negligence?

My mother was prescribed coumadin medication by her cardiologist that she was told to discontinue by an ER physician after a fall with damage to her head. She called her cardiologist to discontinue coumadin. He continued prescribing it, and mother''s memory began failing her. As her memory failure increased she resumed taking the coumadin, without monthly blood level testing or monitoring by her doctor''s office. She suffered a brain hemmorage that ended in her death. While still alive in the ER her CT scan showed an INR level of 5.11. The therapeutic level was to remain between 2.50 -3.00. To me that is an obvious negligent comission of patient directives and omission of proper prescriptive care. Any help would be appreciated. Thank you.