actually i think she says it twice. somebody obviously messed up in the editing of the audio track. and as you pointed out, even if she said it just once, who the heck was she saying it to, and why?????
Yeah, she says it twice ... for no apparent reason, but I agree its likley a minor editing glitch. It's also the scene of another voice-over. The line "What can we do about him?" (as she throws the light bulb against the wall) was clearly dubbed-in later on.
She laughs at the fact that Columbo brought the burnt out bulb with him and practically scolds him in the same breath. Weird one. Susan Clark did a terrific job.