It was on LivePD last night (guilty pleasure). Clerks are mother and daughter. I think they mostly got lucky, there wasn't a ton of skill involved. But, protip: most civilian defensive shootings don't really require a ton of masterful gun handling or marksmanship.
The revolver ran dry (5-shot), which was extremely lucky when the robber got the gun off the older clerk, and tried to shoot her with it. Also, it being a 5-shot means it's likely a .38. A .22LR snub doesn't have that much muzzleflash, either. If you look closely, you can pretty plainly see the gun recoiling at the 1-minute mark.
Agree the shot when struggling was risky. But she at least had the wherewithal to keep the still-loaded pocket pistol out of the guy's reach, instead of moving in to tussle. She really should have shot him before it got to that point.
Even better was the use of cover. The guy came around the counter and pretty much walked into an ambush.
What was really friggin' stupid was locking him in to begin with. Guy's got the money, he wants to leave, great, go ahead.