I don't know exactly what all the conditions you mention mean, I do noticed that you have a condition in common with your mum and that you have to get blood tests every 6 months. Do you get your tests? Apparently it is important.
It is totally understandable how you feel right now. Maybe treatment would have made your mum live longer, maybe it wouldn't have. She lead her life the way she wanted to and obviously that is difficult to accept right now. It was not possible for you to be there every time she needed calming down, if you wouldn't have been at the gig you would have been at work perhaps, you don't have to feel guilty about it (tho I understand that is difficult).
I hope your brothers can give you some support, a big hug from me too .