"Her books are ten."
What is this intended to mean? If it is meant to say that "she has ten books" then that would be the translation to English. Or you could say "She owns ten books". Her books are ten is not a phrase that would appear anywhere in the English language. The only way the phrase would make any literal sense would be if you were trying to say that all of her books are ten years old. And, really, why would you be wanting to say that?