Personally, I'd probably just translate it directly as "Manolo and the Valkyrie." Valkyries are generally represented as beautiful women, and because they're associated with a (still very popular) ancient mythological tradition, they sound quite exotic even to most English speakers. I would say that "Valkyrie" is probably the best word for talking about a blonde, European-looking woman but also suggesting that she seems exotic, mysterious, and perhaps supernatural.
It's true as Jennifer says that Valkyries are also associated with battle and death... but that's surely true, to some extent, of the Spanish title, too, since the author is using the very same word. And "Amazon" is certainly an equally battle-charged word.