Exactly. This is one of the main things that we've bred cats for -- exterminating vermin. (The worms are just a toy, from Tiger's perspective.) The correct reaction is to tell her that she's a mighty hunter, praise her to high heaven, and then say, "Thank you, but I'm not hungry right now. I'll save it for later." (Cats understand left-overs.) Then, when she's not looking, you flush it down the toilet or otherwise dispose of it. And if you don't want it to happen again, you keep your cat inside, and hope that your house is mouse-proof.
Sweet Thing once killed a mother mouse and brought the entire litter of baby mice to me, one at a time, to take care of. There was nothing I could do for them except give them a quick death. Infants don't smell the same as adults, in any species, so a cat may not see them as prey (though, in the wild, other predators see infants as easy pickings).
Margret
