Barbara Baylor is a murderess and secondary villainess in the episode "Caution: Murder Can Be Hazardous to Your Health". However, she is no prey for Lt. Columbo.
In Washington D.C. in 1988, she made a plan with her husband, a Dr. Baylor, to fake his death by murdering a man. The plan was to wait for their victim, Duke Dimarco, to become high on drugs. Once that happened, Barbara would give her husband the signal to enter Duke's apartment and give him a fatal overdose of poison. Once Duke was dead, the doctor and his wife would take Duke to the doctor's own car and push it over a cliff. Once the car exploded, the body would be unidentifiable (Dr. Baylor and Barbara had a rental car waiting by said cliff which would allow them to flee the scene once the car was destroyed). Once the deed was done, Dr. Baylor would flee the country to somewhere in Europe, and Barbara would join him once she collected his life insurance policy and "live happily ever after".
Unfortunately for the good doctor, Barbara fell in love with Duke, and decided she'd rather spend the rest of her life with him. So she flashed Dr. Baylor the signal, letting him come up to Duke's apartment. However, instead of being high and easy to kill, Duke was very much sober and snuck up on Dr. Baylor, choking him unconscious and allowing Barbara to inject him with whatever he was going to inject into Duke. Presumably due to the police quickly deducing Barbara as the killer of her husband, she did not collect the insurance money and couldn't leave the country. Instead, she and Duke likely roamed across the US, eventually winding up in Los Angeles, California.
This murder was reenacted for the television show Crime Alert!, a program similar to America's Most Wanted. Her story being on the show soon led to someone spotting her in a cheap motel with Duke. Crime Alert! quickly reported on the story and filmed at the motel, where police arrested Barbara and Duke, bringing her to justice.
Ironically, the host of Crime Alert!, Wade Anders, would also be arrested for the murder of newscaster Budd Clarke shortly after she and Duke were captured.