None of your points matter for self-defense. A jury might find her sympathetic and deliver a "not guilty" but legally you can't self-defense after the fact.
She's 92, what are you really going to do to her?
I could see a conviction, and sentencing with a recommendation for a specific place with facilities for elderly "residents".
Makes me wonder how many times in those 72 years did her son do something to cause her to reach for the pistol but not pull it out. This time he kissed the baby.