Dalk kom my vriendin ook op Sondag, as sy nie by haar werk is nie.

Afrikaans main clauses usually follow the verb-second rule. That means the finite verb comes in the second position, no matter what comes first.

So in:

Dalk kom my vriendin ook op Sondag ...

the first element is Dalk. Because that takes the first slot, the verb kom must come next, and the subject my vriendin comes after it.

Compare:

• My vriendin kom ook op Sondag.
• Dalk kom my vriendin ook op Sondag.

Both are correct. The difference is just what is placed first for emphasis.

Dalk means maybe or perhaps.

It shows uncertainty:

• Dalk kom sy. = Maybe she is coming.
• Dalk reën dit. = Maybe it is raining / it may rain.

In this sentence, Dalk suggests that the speaker is not sure whether the girlfriend will come.

Ook means also or too.

In:

Dalk kom my vriendin ook op Sondag ...

it means that the girlfriend may come as well.

Its position is normal for Afrikaans. Ook often comes before the part that follows it, or in the middle of the clause where it sounds natural. Word placement with ook can shift a little depending on emphasis.

For example:

• My vriendin kom ook op Sondag. = My girlfriend/female friend is also coming on Sunday.
• Ook my vriendin kom op Sondag. = Even my girlfriend/female friend is coming on Sunday.
  This is more marked and more emphatic.

It can mean either, depending on context.

• vriend = male friend / boyfriend in some contexts
• vriendin = female friend / girlfriend in some contexts

Afrikaans often relies on context to show whether the meaning is romantic or simply friendship. So my vriendin could mean:

• my girlfriend
• my female friend

If the meaning has already been given to the learner, then that context decides it.

Op is the normal preposition for days of the week in Afrikaans, just like on in English.

So:

• op Maandag = on Monday
• op Sondag = on Sunday

That is the standard way to express the day something happens.

In Afrikaans, names of the days of the week are capitalized:

• Maandag
• Dinsdag
• Woensdag
• Donderdag
• Vrydag
• Saterdag
• Sondag

So Sondag is capitalized because it is the name of a day.

Here as means if.

So:

as sy nie by haar werk is nie

means:

if she is not at work

Afrikaans as can be tricky for English speakers because it can appear in different meanings depending on context, but in this sentence it is the conjunction if.

The comma marks the start of a subordinate clause:

Dalk kom my vriendin ook op Sondag, as sy nie by haar werk is nie.

The part after the comma gives the condition: if she is not at work.

Afrikaans often uses commas to separate this kind of extra clause, especially when it follows the main clause.

Because as introduces a subordinate clause, and in Afrikaans subordinate clauses the finite verb usually moves toward the end.

Compare:

• Main clause: Sy is by haar werk. = She is at work.
• Subordinate clause: ... as sy by haar werk is. = ... if she is at work.

So in your sentence:

as sy nie by haar werk is nie

the verb is appears near the end because the clause is subordinate.

Afrikaans normally uses double negation.

So to say not, Afrikaans often uses:

nie ... nie

In this sentence:

as sy nie by haar werk is nie

the first nie introduces the negation, and the second nie closes it.

This is one of the most important grammar patterns in Afrikaans. English has only one not, but Afrikaans usually needs two nie words in a full negative clause.

A simple example:

• Sy werk. = She works.
• Sy werk nie. = She does not work.

But in longer clauses, especially subordinate ones, the second nie still comes at the end:

• Ek weet dat sy nie vandag werk nie. = I know that she is not working today.

Literally, by haar werk is something like at her work.

In natural English, that usually becomes:

• at work
• at her workplace
• sometimes at her job

Here:

• by = at / by
• haar = her
• werk = work, job, workplace

So sy is by haar werk means she is at her place of work.

Because they have different grammatical jobs.

• sy = she
• haar = her

In the clause:

as sy nie by haar werk is nie

• sy is the subject: she
• haar is a possessive/determiner before werk: her

So:

• sy kom = she comes
• haar werk = her work

This is similar to English:

• she is not at her work

Afrikaans normally does not use die before a day of the week in this kind of time expression.

So the normal form is:

• op Sondag = on Sunday
• op Maandag = on Monday

Using die would sound more specific or marked, and is not the usual basic pattern for saying when something happens.