Starring Kate Mulgrew as Kate Columbo (Columbo actually referred to her as "Rose Columbo" on his show, a discrepancy that is never explained) the show never features Mr. Columbo.

That could explain why the show wasn't as successful as had been hoped. NBC tried everything to make the show successful, it even tried using three different show titles:
The aforementioned Mrs. Columbo:
Then, after a divorce from Mr. Columbo, it was Kate Loves a Mystery:
And lastly, Kate the Detective:
Amazingly, the show lasted less than a full season, going through all of these name changes in just 16 episodes.