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I think that you have two things going on here-

1. Someone probably backed out the screw that tensions the mainspring or cut down the spring to get a lighter trigger pull.
2. The woman did not have the arm strength to hold the revolver against the recoil of the first shot.

Because what happened, if you look closely at the video, she “Fanned” the pistol. Her trigger finger never moves off of the trigger. The hammer rebounds and the cylinder rotates and the hammer drops again. She held the trigger back and the recoil did the rest. That can be caused, in a heavy recoiling revolver, by a too light mainspring or one that has been messed with.