Why is it hendes instead of hende?
Hende means "her" (the object form of "hun" (she)). For example: Jeg elsker hende = I love her
Hendes is the possessive form of "she/her" ("her(s)"). For example: Han elsker hendes bøger = He loves her books; Bøgerne er hendes = The books are hers
Is "sin elefant spiser brød" not right?
It's noit right because sin always has to refere to a subject.
An example to compare please...