I don't like the nickname
Len on a girl. I think it's brilliant as a nickname for
Leonard or
Lennon (or several others), but on a girl it sounds...weirdly masculine in a way I don't like.
My favourite nickname for
Gwendolen (which I prefer, though I pronunce both
Gwendolyn and
Gwendolen the same way) is currently Gwendy. While it looks stupid written out, I like how it sounds.
Gwen and Gwennie are my lest favourites, after
Len.
Wendy is probably my favourite of your list.
Gwendolen could also become a Wennie, a
Winnie (like in The Wonder Years--Winnie
Cooper was a
Gwendolyn, IIRC), or a
Dolly. I like all of those nicknames (particularly
Winnie) a great deal, too.
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