Hun siger godnat.

Because hun is the subject form of she.

In Hun siger godnat, hun is the person doing the action, so Danish uses hun.

Compare:

• Hun siger godnat. = She says goodnight.
• Jeg ser hende. = I see her.

So:

• hun = she
• hende = her

Sige is the infinitive form, meaning to say.

In a normal present-tense sentence, Danish uses the present form siger:

• at sige = to say
• jeg siger = I say
• hun siger = she says

A very useful point for English speakers: Danish verbs do not change for different persons in the present tense.

So you get:

• jeg siger
• du siger
• han siger
• hun siger
• vi siger

The verb stays siger every time.

In this sentence, the receiver is simply not mentioned.

Hun siger godnat is a complete sentence and means that she is saying goodnight, without saying to whom.

If you want to include the person she says goodnight to, Danish often uses til:

• Hun siger godnat til børnene. = She says goodnight to the children.

So the short version is:

• Hun siger godnat. = the listener/receiver is unspecified
• Hun siger godnat til ham. = the receiver is specified

Yes. Godnat is normally written as one word in modern Danish.

It is a fixed expression meaning goodnight.

This is similar to how some expressions become set forms in a language. Even though it historically relates to god + nat, the standard form here is godnat.

You will commonly see:

• Godnat! = Goodnight!
• Hun siger godnat. = She says goodnight.

Because godnat here is not being used as a regular countable noun. It functions as a set expression or formula that someone says.

English can also do this in a similar way:

• She said goodnight.

You would not normally say:

• She said a goodnight.

So Danish works the same way here: godnat appears without an article.

A rough learner-friendly guide is:

• Hun ≈ hoon / hun with a short vowel, but the Danish u is different from English
• siger ≈ SEE-er or more naturally si-er, with a soft g
• godnat ≈ go-nat or goð-nat, depending on how carefully it is said

A few pronunciation notes:

• In siger, the g is usually soft, not a hard English g.
• In natural speech, siger often sounds like two syllables: si-er.
• In godnat, the first part may sound less like a full English god and more softened.

A broad approximation could be:

hun SEE-er go-NAT

But listening to native audio is especially helpful here, because Danish pronunciation is much less phonetic than spelling suggests.

It can mean either, depending on context.

The Danish present tense often covers both:

• She is saying goodnight / She says goodnight
• She says goodnight every evening

So Hun siger godnat could mean:

1. right now: she is in the process of saying goodnight
2. habitually: she says goodnight as a regular thing

Context tells you which meaning is intended.

The normal neutral word order is:

• Hun siger godnat.

That is the standard subject + verb + object/expression order.

But Godnat siger hun is also possible, with a different emphasis. It sounds more marked and can be used when focusing on godnat.

For example, it might feel like:

• Goodnight, she says.
• It’s goodnight that she says.

So:

• Hun siger godnat. = neutral
• Godnat siger hun. = more literary, emphatic, or context-driven

In standard modern Danish, the usual form for goodnight as a farewell is godnat as one word.

So for this sentence, write:

• Hun siger godnat.

Writing god nat would generally not be the normal choice here.

For a learner, the safest rule is:

• use godnat for the expression goodnight
• treat it as a fixed word

It usually comes after godnat, often introduced by til.

Examples:

• Hun siger godnat til sin mor. = She says goodnight to her mother.
• Hun siger godnat til børnene. = She says goodnight to the children.

So the pattern is often:

Hun siger godnat til + person

This is a very useful expansion of the basic sentence.

Yes, it is very natural.

Danish often uses sige with fixed expressions that people say aloud, and sige godnat is one of them.

Common examples include:

• sige hej = say hi
• sige tak = say thanks
• sige undskyld = say sorry
• sige godnat = say goodnight

So this sentence is simple, normal, and idiomatic Danish.