Plus, near the beginning when she made a fishing net, she said that as long as she had the base materials and understood somethings structure she could use creation at a discount. While she could use storage to separate the salt from the water, she should be able to achieve the same with creation, so I don't think she's making salt from nothing, like with the onigiri, but rather using creation to create salt with salt water
Daghhh I'd hoped with the beach setting she'll delve into seafood cuisine, I love when this manga goes all shokugeki with it. Also damn she looks badass with the dagger conjuring from her palm, reminds me of Anri Sonohara