Haar idee was goed, en die onderwyser het haar voorstel gebruik.

Because both instances mean her.

• Haar idee = her idea
• haar voorstel = her proposal/suggestion

In this sentence, both are possessive forms, because each one comes before a noun.

A useful thing to know is that Afrikaans often uses haar for both:

• her as a possessive: haar boek = her book
• her as an object pronoun: Ek sien haar = I see her

So Afrikaans does not make the same spelling distinction that English does between her and her.

Was is the past tense of wees = to be.

So:

• is = is
• was = was

In Haar idee was goed, the speaker is describing something in the past, so was is the natural choice.

This is also worth noticing: Afrikaans often uses a simple past form with wees:

• Dit is goed = It is good
• Dit was goed = It was good

Because goed comes after the verb was and is acting as a predicate adjective.

Compare:

• 'n goeie idee = a good idea
  
  • adjective before the noun
• Die idee was goed = the idea was good
  
  • adjective after the verb

So in this sentence:

• Haar idee was goed = correct

If you moved the adjective in front of the noun, then you would usually get:

• haar goeie idee = her good idea

This is a very common Afrikaans past-tense pattern.

• het = auxiliary verb, like have
• gebruik = past participle/main verb at the end

So:

• die onderwyser het haar voorstel gebruik
  literally something like the teacher has used her proposal but in normal English here it is translated as the teacher used her proposal

Afrikaans very often uses this het + past participle structure for completed past actions, even where English would simply use the simple past.

Because in Afrikaans main clauses, the finite verb usually comes in the second position, and in a perfect construction the main verb often goes to the end.

So the pattern is:

• subject
• het
• other information
• main verb at the end

Here that gives:

• die onderwyser = the teacher
• het = has/used auxiliary
• haar voorstel = her proposal
• gebruik = used

That word order is very normal in Afrikaans.

Because die means the.

So:

• die onderwyser = the teacher
• 'n onderwyser = a teacher

Afrikaans uses die as the definite article for singular and plural nouns. It does not change for gender the way articles do in some other languages.

Not in the same way as languages like German or French.

In this sentence:

• die stays die
• adjectives do not change for masculine/feminine gender
• the noun idee does not have a special grammatical gender that affects the article

The only gender-related meaning here is natural gender in haar, which tells you the person is female: her idea, her proposal.

Here voorstel is a noun meaning proposal, suggestion, or sometimes plan/idea put forward.

So:

• haar voorstel gebruik = used her proposal / used her suggestion

Be aware that voorstel can also be a verb in other contexts, meaning to propose or to introduce. But in this sentence it is clearly a noun because it is part of the noun phrase haar voorstel.

Traditionally, onderwyser can mean a male teacher, and onderwyseres can mean a female teacher.

But in many contexts, onderwyser is also used more generally for teacher, especially if the gender is not important.

So in this sentence, die onderwyser is best understood simply as the teacher, unless the wider context makes the teacher specifically male.

Because en is a coordinating conjunction, like English and.

After a coordinating conjunction, the next clause usually keeps normal main-clause word order:

• die onderwyser het haar voorstel gebruik

That is why the verb het is still in the normal second position.

This is different from some subordinating conjunctions, which can change the word order more strongly.

Yes, it is basically a cognate.

• idee = idea

The spelling is slightly different, but the meaning is very close and easy for an English speaker to recognize.

That is true for several words in the sentence:

• idee = idea
• goed = good
• gebruik = use/used, though less obviously similar
• voorstel = proposal/suggestion, not a direct English lookalike but common in Afrikaans

No, not if the meaning is her.

• sy usually means she
• haar means her

So:

• Sy het gekom = She came
• haar idee = her idea
• Ek sien haar = I see her

In your sentence, the person is female and the meaning is possessive, so haar is the correct form.

Yes, it can be.

The sentence joins two full clauses:

• Haar idee was goed
• die onderwyser het haar voorstel gebruik

A comma before en is often used when two independent clauses are linked and the writer wants a clear pause or separation.

So the punctuation here is natural and easy to read.