Hitch-hiker -- S4E09 (clip)
Annoyingly for such a classic clip (I've seen short versions of this for about ten years!) I can't find a cast list for it, or indeed anything beyond this being an episode called "Room Service" from an anthology show also known as A Scare At Bedtime. Anyway, a gorgeous woman finishes off both her partner in crime, and their foe, with a silenced pistol and a winning look...
For a list (and description) of many more lethal lady clips that can be do