I "think" the shell casing ended up on the floor. Nonetheless, sink or floor, I posted a few days ago about how the gun could have jammed if JA didn't hold a firm enough wrist when she shot. This would have kept the spent shell casing from being ejected, causing a jam. If she then worked him over with the knife then came back for the gun and cleared the spent casing out (unstuck the gun), the cartridge would have then been ejected. Shot comes at the beginning of the attack, cartridge ejected after. Possible.
Edit, add link:
Limp wristing - Wikipedia, the free encyclopedia
Edit, from the above link: One common result of limp wristing is a failure to eject, as the slide will be moving too slowly at the point where the ejector is activated. The slow moving case will be caught as the slide closes, resulting in a stovepipe jam.
Just an opinion.