The umbrella man shot the dart that hit his throat and released paralyzing toxins
Jackie then administered the kill shot
If Oswald fired, it was the shot that his Connally
There are some frames removed but if you watch the film closely you can still see a stunted progression of her pulling tghe gun back down and toward her purse. She then realizes that the casing was ejected onto the rear deck lid of the Lincoln and climbs onto the deck lid to retrieve it.
oh she definitely was not alone. In fact i think she was the fail-safe. She saw that either Oswald or someone from the front missed and hit Connally and then she was forced to shoot. You can see her pausing after JFK has been incapacitated by the poison fleshette while she looks at Connally and then decides she has to act. In my mind there were many people involved. Police, feds, state, city officials, media, wealthy power brokers, etc, in other words the cabal