Names that Enid used less frequently?

[jubei]

Zerelda Brass , the American girl from Malory Towers. I also remember her name as it sounds much like a RPG game character. Zerelda should be even used lesser in real world I suppose.

[Blytonfan]

Claudine - from St. Clare's
Wilhelmina - from Malory Towers

And I haven't come across any modern-day "Winifreds"

[Barnard]

There was a second Wilhelmina, but used as a middle name.
In Secret Seven Mystery, the missing girl’s name is Elizabeth Mary Wilhelmina Sonning.

[Blytonfan]

Interesting. A Wiki search says "Wilhelmina (also: Wilhelmena, Wilhelmine, Wilhemina) is a feminine given name, the Dutch, German and Yiddish form of Wilhelm or William, which is derived from the Germanic wil, meaning "will, desire" and helm, meaning "helmet, protection"."