You don't hear much from her because she's been dead for 17 years. She died in 1998 from a heart attack in LA.
Not according to the Internet Movie Database and a general web search. Interestingly enough, her final screen performance was in "Troubled waters," so I figure her vanishing act had more to do with having simply left acting. In fact, I was curious enough about what had become of her myself some time ago, and found a photo of her taken in 2003, which I then posted here.
I just watched her perform @ Indian Wells Resort Hotel with her long-time pianist Rich Bono tonight. She sings and moves exactly as she did when she appeared in Columbo. They are regular performers there on most Wednesdays. They do take a break from time to time.
In a later scene, Columbo and Danziger enter a bar where a recording of "When the World Was Young" is playing. The voice sounds like Poupee Bocar. Perhaps they recorded it for the club scene and decided not to use it there but didn't want to waste it.