Isn't sassy very different depending on the person/ subjective? There are some names here that I would never even consider to be sassy such as Heidi and Nina.
And I dislike the idea that for a girl name to be sassy or powerful it needs to be a boy name.
To me sassy means bold, non-nonsense, outgoing, super-confident and showing attitude. And this means a famous namesake such as Cleopatra, Medea, Luna, Scarlett, Coco, Carmen, Bellatrix, Boudicca, Matilda. Think of Greek goddesses, female warriors, explorers, badasses.
It could also be any name starting with Q, X or Z. Xanthe, Queenie, Zadie. Or power of nature such as Tempest.