We're back at the Denbrow (I've also seen it spelled Dembro at the IMDb.com) ranch for a "Born To Re-Run" suggestion. Sheila Denbrow was 19 when she married widowed rancher John Denbrow and became step-mother to his daughter "Johnnie". But a few years of this hard life became too much for her, and she looked for any chance of escape - even if it was a fleeting afternoon of passion with some passing drifter or one of the hired cowhands. (That's the impression I got anyway; I don't think 'Cheyenne' was her first attempt to cheat on her husband. But Cheyenne was probably the first to refuse her advances.)
Sheila's desire for Cheyenne was also fueled by her realization that Johnnie had grown up to be a beautiful 17 year old and that she was a rival for the attentions of Cheyenne Bodie. Her unrequited lust, long-simmering anger at her situation, and insecurities about her aging looks led her to a very dark place in her mind. And so, on a night of celebration when her husband passed out drunk in the carriage inside the barn and she accidentally tipped over the lantern, setting the hay ablaze, Sheila Denbrow made the decision to leave John in there to his doom.
As time passed, the guilt became overwhelming; she became fixated on flames and kept hearing the screams of the horses. (Even though they survived, their cries became a substitute for those her husband could never utter.) Sheila Denbrow developed what Barney Stinson would say was a bad case of "crazy eyes", and she finally died when she was run down by the horse of rival rancher Martin Storm, who was trying to drag-lynch Cheyenne.
It's the contention of Toobworld Central that her soul was eventually reincarnated as Nora Chandler, a famous actress from the 1950's. Although she had no conscious remembrance of the events in that past life, it now became easier to accomplish the same results as Sheila did.
First, she murdered her husband; then years later, she killed her assistant, the only other person who knew what she did. (Although not stated in the 'Columbo' episode "Requiem For A Falling Star", I believe Nora's assistant was the young woman who had been having the affair with Nora's husband when they were discovered by the actress.)
And how did Nora kill her assistant? By setting fire to her car while she was in it.
Like I said, past life experience made it easier to do such heinous acts.
At least, that's my theory......