"Lovely But Lethal" has never been one of my favorite episodes because I've always felt that Vera Miles, who is a good actress, was miscast in the role. One thing that I never understood was why they made her wear such an obviously bad looking red wig that really didn't match her face well. (There are plenty of other guest shots of Miles as she really was in this period and she looks a lot more attractive with her own hair IMO)
Only now do I realize why Miles wears a red wig. The character of Viveca Scott is actually meant to resemble actress Arlene Dahl, a redhead who by the 1970s was no longer doing much acting but had become famous in the cosmetics world herself. I wouldn't even be a bit surprised if Dahl was the one they initially wanted to play the part because it would have been much like with Johnny Cash, a case of the performer playing a version of themselves.