I always think she's an example of what they call "Hollywood Homely" (or a few similar phrases). In other words, she's meant to be this comical "starched" female office worker, but she's also very attractive, just as Pino say.

Heh! Yes, the classic move is where the "plain" woman takes off her glasses and unpins her hair (in a bun) so that it falls to her shoulders, and the guy says something like, "Why, Miss Jones...You're beautiful."

In "Columbo" maybe the most prominent example of the woman who is supposed to be "plain" when any man can see that she is actually very beautiful, is Karen Fielding (Julie Harris) in "Any Old Port in a Storm".

Also, we are supposed to see one of those beauty "transformations" of the killer in "Lady In Waiting," but for me her "beauty" makeover and new wardrobe are just too laughable to be anything but funny.

Actually, I'm very sentimental about ' 60s and early ' 70s women's fashions, and the more stereotyped and "out there," the better!
But I don't think the things she ends up wearing exactly "suit" Susan Clark / Beth Chadwick, so I agree with you there.