Succinylcholine is widely used in operating rooms. It causes paralysis of every muscle in the body, except for the heart. A tiny amount of the drug will be effective. Once the shot is administered, the person collapses. They are conscious, they can see, but they can't move a muscle. Their heart continues to beat. And they suffocate. It takes a minute or two, and they are unconscious, a few more minutes they are dead.
It is difficult to test for but supposedly traces can be found by a good lab.
The problem is, if Mom hit everybody with a shot of this stuff, fine they would all drop where there were when they got the shot. But when Mom gave herself the shot, the syringe would be right next to her on the ground she would have been unable to throw it.
You know way more about that drug than I do. You don't think that whoever administers an injection would have a few seconds to toss the syringe into the bushes? As someone who has spent a good bit of time searching in grass for cartridge cases I know they can hide pretty well.
Patriotism (and religion) is the last refuge of a scoundrel.
