I think this is the first drama I have seen where the FL cook has a pretty bad work ethic. I really don't understand…
It's possible that the Head Chef feared that she will replace him, therefore he wasn't allowing her to cook. It makes sense why she had to hide in the storeroom to make food for fellow co-workers. Or perhaps, she learnt to cook from her grandfather instead of going to a professional school. So, she doesn't have valid credentials, and they underestimate her. Anyway, the way she talks while cooking shows she understands ingredients better.