Espérance does mean "
Hope" in French and is used (albeit very, very rarely) as a variant of
Esperanza. It is more commonly used as a soccer club/company/organisation type name like English speakers may use words like Quality, Freedom or other positive words that don't carry the same name associations as
Hope or
Constance.
Of course, not many people in the US would make that association. You may get some confused looks if you live in a city with a large Hispanic community because of the spelling, since
Esperanza is a way more common name.
As far as I know
Nancy is not a common nickname for Esperanza/ance; Espie or Esper being the usual ones. But, hey, it's your kid and you can nickname her Butterball Turkey if you want ;)