As they noted, she was very much of her time. But she was as well known then as, say, Paris Hilton is today (although in a much cleaner way - it WAS the 50s after all). Let's put it this way - the pointy-rubber-cone bumpers on the front of some 50s cars were known as Dagmars, and that tells you a lot about how she became popular. Happily, from all I've read, she seems to be a nice, down-home person.
And only in this group would you get a pass on not knowing Dagmar, but not on not knowing Jerry Shaw.