Hun har god samvittighet.

Not necessarily. In Norwegian, especially after å ha, abstract nouns are often used without an article when you are describing a general state or condition.

So Hun har god samvittighet is the normal, idiomatic way to say that she feels morally clear.

Compare:

• Hun har god samvittighet = she has a clear conscience
• Hun har en god samvittighet = grammatical, but less idiomatic and more descriptive

This article-less pattern is common in Norwegian:

• ha dårlig tid
• ha rett
• ha ansvar
• ha god samvittighet

Because adjectives in Norwegian must agree with the noun.

God is used with singular common/feminine nouns.
Godt is used with singular neuter nouns.
Gode is used with plural and often definite forms.

Since samvittighet is not a neuter noun, god is the correct form.

Examples:

• en god stol
• ei god bok
• et godt hus
• gode bøker

So here:

• god samvittighet = correct
• godt samvittighet = incorrect

Samvittighet is a feminine noun. In Bokmål, feminine nouns can often also be treated as common gender, so you may see either:

• ei samvittighet
• en samvittighet

In this sentence, that does not change the adjective form: it is still god.

Also, many nouns ending in -het are feminine in Norwegian.

Har is the present tense of å ha, which means to have.

So:

• å ha = to have
• har = have / has

In this sentence, Hun har ... means She has ...

Other forms:

• hun hadde = she had
• hun har hatt = she has had

Literally, it is good conscience, but in natural English the usual equivalent is often a clear conscience.

So even though the Norwegian uses god, the best English translation in many contexts is:

• She has a clear conscience

This is a very common Norwegian expression, and it often refers to not feeling guilty.

Yes, it is grammatical, but it sounds less natural if you simply mean she has a clear conscience.

The version without the article, Hun har god samvittighet, is the standard idiomatic expression.

Using the article can sound more like you are describing her conscience as a thing or quality:

• Hun har en god samvittighet

That is possible, but it is not the most usual way to express the idea.

Because god and bra are not always interchangeable.

Both can mean good, but Norwegian uses god samvittighet as the established expression.
Bra samvittighet would sound unnatural to most speakers.

A useful rule for learners is:

• bra is often used for something being good in a general or practical sense
• god is often used in fixed expressions and with many nouns describing qualities, feelings, or states

So you should learn god samvittighet as a set phrase.

The usual opposite is dårlig samvittighet.

• Hun har dårlig samvittighet = she feels guilty / she has a bad conscience

This is a very common expression in everyday Norwegian. In many situations, English would simply say she feels guilty.

So:

• god samvittighet = clear conscience
• dårlig samvittighet = guilt / bad conscience

To make it negative, add ikke:

• Hun har ikke god samvittighet.

To make it a yes/no question, put the verb before the subject:

• Har hun god samvittighet?

That is standard Norwegian word order:

• statement: Hun har god samvittighet.
• question: Har hun god samvittighet?

No. This is a very basic Norwegian main clause:

• Hun = subject
• har = verb
• god samvittighet = object/complement-like phrase after the verb

So the pattern is the normal subject + verb + rest order:

• Hun har god samvittighet.

It is a good example of simple Norwegian statement word order.