Do we have a case? Where should we start?

Aunt taken to hospital with vomiting, fatigue, and severe headache. Hospital diagnosed blood clot in the leg and said she needed to be released. We insisted she needed a neurologist and MRI for severe headache. Hospital said no and send to rehabilitation center. While at center she had more severe headaches, nose bleed, double vision, and more vomiting. Doctor at the center said she was fine. We took her on our own to a neurologist who looked at her for five minutes and said she needed to go to ER. Rehabilitation center said she was fine and they would not send an ambulance. Neurologist had to send one. In hospital they found a brain tumor and bleeding in the brain (most likely from the blood clot medication). She is now in hospice because this was caught too late. We don't know what to do but, feel that we need to do something so someone else does not have to go through the agony my aunt did.