Hún neitar að koma.

Because hún is the subject form of she.

Icelandic pronouns change form depending on their role in the sentence:

• hún = she (subject)
• hana = her (object, accusative)
• henni = her (dative)

In Hún neitar að koma, she is the one doing the action of refusing, so the subject form hún is required.

Neitar is the 3rd person singular present tense form of the verb að neita.

So:

• að neita = to refuse / deny
• ég neita = I refuse
• þú neitar = you refuse
• hún neitar = she refuses

The ending -r is very common in present-tense forms in Icelandic.

Here að is the infinitive marker, like English to before a verb.

So:

• að koma = to come

In this sentence, neitar að koma means refuses to come.

Be careful: að can also be a conjunction meaning that in other sentences, but here it is simply marking the infinitive.

Because after neita in this meaning, Icelandic normally uses an infinitive phrase:

• neita að + infinitive

So:

• neitar að koma = refuses to come
• neitar að fara = refuses to go
• neitar að hjálpa = refuses to help

The verb after að stays in the infinitive form.

Not always. Að neita can mean both:

• to refuse
• to deny

The exact meaning depends on what follows.

For example:

• Hún neitar að koma. = She refuses to come.
• Hún neitar þessu. = She denies this / refuses this.

So the verb is broader than just one English translation.

This is the normal Icelandic main-clause order:

• subject + verb + infinitive phrase

So:

• Hún = subject
• neitar = finite verb
• að koma = infinitive phrase

That gives a very natural neutral sentence.

Yes. Icelandic is a verb-second language in main clauses, which means the finite verb often comes second.

If you move another element to the front, the verb still stays in second position:

• Í dag neitar hún að koma. = Today she refuses to come.

Notice that when Í dag comes first, neitar still stays second, and hún moves after the verb.

A rough pronunciation guide for an English speaker might be:

• Hún ≈ hoon
• neitar ≈ nay-tar
• að ≈ short ath / ahth with a voiced th
• koma ≈ ko-ma

A few notes:

• ú is a long oo sound.
• ei is pronounced like ay in day.
• ð is like the th in this, though in fast speech it can be weaker.

A rough full approximation: hoon NAY-tar ath KO-ma

It is literally to come, but just like in English, the exact sense depends on context.

It can mean:

• to come physically
• to arrive
• to show up

So Hún neitar að koma could mean:

• she refuses to come
• she refuses to arrive
• she refuses to show up

The broader situation tells you which English phrasing sounds best.

Yes, but it changes the nuance.

• Hún neitar að koma. = She refuses to come.
  This is the simple present and is the most neutral version.

• Hún er að neita að koma. = She is refusing to come.
  This emphasizes an ongoing action or current situation.

So both are possible, but the original sentence is simpler and more basic.

You usually add ekki:

• Hún neitar ekki að koma.

This literally means She does not refuse to come.

That is not the same as She refuses not to come. If English is your first language, it is worth watching how the negation changes the meaning.

In Icelandic, ekki usually comes after the finite verb in a basic sentence like this.

The dictionary forms are:

• hún → pronoun, basic nominative form hún
• neitar → from að neita
• að → infinitive marker að
• koma → from að koma

So if you were looking the words up, the two verb entries would be:

• að neita
• að koma