Don't worry, she'll be ok. I left mine for 8 days without a fish-sitter or food when I went on vacation earlier this month and he was perfectly fine when I got back. Fish-sitters tend to create more problems by overfeeding unless they're up for water changes, too.
I read a breeder's story on another aquarium forum in which he had his shipment of bettas rejected by Brazilian customs and sent back to him in Singapore. The whole process took a little under 4 months, but when he opened the box expecting the worst, every single fish was still alive. This definitely isn't recommending to anyone reading this to leave your bettas without food for this long, but it demonstrates how tough the little guys can be.