I am pretty sure that Eleanor (& variants) and Elena are completely different names
.
Altough I have met a couple of Eleanors and what I initially heard was "Elena" (pronounced like Helena without the "h"), so I assume that's why many people think they are the same name.
I have just looked it up on the Oxford Names Companion, and it says:
"Eleanor (variants Elinor, Ellenor) - English: from and Old French spelling of the Old Provençal name Alienor, which has been taken to be a derivative of Helen, but is probably of Germanic derivation (with a first element 'ali' - other, foreign). The names was introduced to England by Eleanor of Aquitaine".
Elena is simply defined as "Italian and Spanish verson of Helen". This one is Greek in origin and is pronounced 'ehn-LEH-na'
Ellena does not appear at all and it is a comprehensive book, so OP, to answer your question no, it's not a 'standard' spelling. To save hassle to your DD I'd go for 'Elena'.
Now Helena, Ellen, Elena, Helen are all the same name.
HTH