I would contact a med mal attorney in my state and talk to them - people here are not going to be able to tell you whether you have a viable case or not. What burdens and levels of proof, evidence etc will be jurisdiction based. I would not suggest anyone take the word of anonymous online people as to what you will have to prove or show in order to have a viable case. Med mal plaintiff's work is usually (in my jurisdiction at least) done on a contingency fee basis. Something to keep in mind is that the defense attorneys are not going to be nice to you or your mother -so one needs to be willing to be put through some unpleasant questioning and hostile attitude from the defense team.