Learn Icelandic: Af hverju hagar hún sér ekki eðlilega?

The verb að haga sér (to behave) is reflexive, meaning it requires a reflexive pronoun—literally, to behave oneself. In a question, the verb comes first, followed by the subject (hún), and then the reflexive pronoun (sér).

Why is the negation ekki placed after sér?

In questions with reflexive verbs, the subject and the reflexive pronoun are tightly linked to the verb. Because of this, the negation ekki gets pushed to the right, landing directly after sér rather than right after the verb or subject.

How is the adverb eðlilega (normally) formed?

It is built from the adjective eðlilegur (normal). In Icelandic, you can often turn an adjective into an adverb of manner simply by dropping the masculine ending and adding -a.

Since this lesson is about eins og (like / as), how could I rewrite this to say 'like a normal person'?

You can easily replace the adverb eðlilega with an eins og phrase of manner. You would say Af hverju hagar hún sér ekki eins og venjuleg manneskja? (Why doesn't she behave like a normal person?).