If simplicity is nessesary, then I'd say "She's Wonder Woman because she was blessed by the goddesses with their power." Zeus needs to be taken out of the equation, he was never a part of her creation or the mythic landscape that Marston first laid out. His Greek mythology had two main players - Aphrodite and Mars/Ares
Exactly== in the film the only thing that had to change was how she was the Godkiller-- Diana was actually brought to life by the Gods...so Zeus, weakened from the battle with Ares, creates the Island and charges (at least Athena and Aphrodite) with blessing Diana (a godchild of the Gods so to speak) with the last of their power...so that she may end Ares should he survive....