According to the book on names that I have here, Ellen, Eleanor, Elaine, Eileen, Aileen, Eilidh, Elen as well as many other simiar names, are all variants of Helen.
Nell and Nellie are considered to be the pet forms of both Helen and Eleanor - and that's from one who ought to know

Apparently Nell Gwynne - perhaps the most famous bearer of the name - was actually Elinor.
Nell