Why bother with thumb cocking??? This is not Camp Perry, . . . this is a bg within sniffing distance, . . . needing to be snuffed instead of sniffed.
I am not sure how it is done, . . . but I have seen DA revolvers that ol' arthritic Aunt Jenny could have poked holes in a bg with, . . . it's all in doin what needs to be done to the trigger mechanism.
Plus, . . . I have abosolutely NEVER shot a .38 short barreled revolver that wasn't louder than an ADHD 3 year old. When the bg hears that, . . . and hears hot lead coming at him, . . . maybe thumb cocking won't be necessary.
As an aside, . . . if she has arthritis problems, etc. a speed loader is an absolute present from an angel.
May God bless,
Dwight