@
Serkket: That's because Mio's Cooking plot is actually a long running one, and turns into a key reason behind her meeting a key person.
@
MNP92: Mio is actually quite a fast learner and did manage to get things alot right on her 2nd attempt (aka., this time there was no non-edible material, and all the materials she used could easily be used for consumption, but needs special technique or process).
Also, Mio actually tries hard and learns things properly; unlike a certain Kijin who is also bad at cooking, but even after many attempts didn't fix her habit or learn anything relating to cooking, only to end-up learning an OP Skill which she uses to make her cooking taste good without much effort.