Learn Portuguese (Portugal): A aluna ainda está meio confusa com a aula. - The student is still kind of confused with the class.

In this sentence, meio is an adverb meaning "kind of" or "somewhat", making it invariable. It only changes to match gender or number when it acts as an adjective meaning "half" (like meia hora for half an hour). Because it modifies the adjective confusa here, it must stay as meio.

In English we would say confused "by" or "about" the class. Why is the preposition com used here?

The adjective confuso strongly pairs with the preposition com in Portuguese when you want to express what is causing the confusion. It literally translates to being confused "with" the class, which is the most natural way to phrase this in European Portuguese.

Could I say um pouco confusa instead of meio confusa?

Absolutely. Um pouco confusa means exactly the same thing. Using meio as an adverb is just a slightly more colloquial and very common way to say "a bit" or "kind of".

Why do we use está instead of é for the student being confused?

We use the verb estar because the confusion is a temporary state resulting from this specific class. If you used ser (saying é meio confusa), it would imply that being a confused or confusing person is a permanent personality trait of the student.