Dok sam čekala u redu, žena ispred mene rekla je da već mjesecima živi u minusu.

Here dok means while:

Dok sam čekala u redu = While I was waiting in line

Croatian dok can sometimes also mean until, but in this sentence it clearly means while, because it introduces an action happening at the same time as the main action.

Sam čekala is the past tense.

Croatian past tense is usually made with:

• the auxiliary biti in the present tense
• plus the l-participle

So:

• sam čekala = I was waiting / I waited
• je rekla = she said

Without sam, čekala by itself is not a normal complete finite verb form in standard Croatian.

Because the speaker is female.

In Croatian, the past participle agrees with the gender of the subject:

• čekao = a man was waiting
• čekala = a woman was waiting

So Dok sam čekala... tells you the person speaking is female.

This is because short unstressed words like sam often follow the first stressed element in their clause. Croatian has special placement rules for these clitics.

So the natural order is:

• Dok sam čekala
• not normally Dok čekala sam

This is one of the most important Croatian word-order patterns to get used to: clitics such as sam, si, je, smo, ste, su tend to come early in the clause, often in second position.

Here redu is locative singular after the preposition u.

• red = line, queue, row, order
• u redu literally = in the line / in the queue

So:

• čekati u redu = to wait in line

Be careful: u redu can also mean okay / all right in other contexts, but here it clearly means in line, because of čekati.

Because the preposition ispred requires the genitive case.

So:

• ja = I
• mene = me / of me (genitive/accusative form, depending on context)

After ispred you use genitive:

• ispred mene = in front of me

Other examples:

• iza mene = behind me
• pored mene = next to me / beside me
• kod mene = at my place / with me

So žena ispred mene means the woman in front of me.

This is another clitic-placement issue.

The auxiliary je is a clitic, and it tends to come after the first whole phrase, not necessarily after the very first single word.

Here the first unit is:

žena ispred mene = the woman in front of me

Then comes the clitic:

• Žena ispred mene rekla je...

This word order is very natural in Croatian.

You may also hear žena ispred mene je rekla, especially in speech, but rekla je is very standard and common.

Because da introduces a subordinate clause, similar to that in English.

So:

• rekla je da... = she said that...

This is a very common pattern in Croatian:

• Mislim da... = I think that...
• Znam da... = I know that...
• Rekla je da... = She said that...

Croatian very often uses da where English may use that or sometimes omit it.

Because Croatian does not do tense backshifting in the same way English often does.

English often says:

• She said that she had been living in the red for months or
• She said that she was living in the red

Croatian normally keeps the tense that fits the situation inside the subordinate clause:

• rekla je da živi...

That means: at the time she said it, this was her current situation.

So Croatian often uses past + da + present where English might prefer a shifted past tense.

Već mjesecima means something like:

• for months already
• for months
• for many months now

The form mjesecima is instrumental plural of mjesec.

Croatian often uses the instrumental plural adverbially to express duration or repeated time over a stretch:

• godinama = for years
• danima = for days
• satima = for hours
• mjesecima = for months

And već adds the sense of already / by now.

So:

• već mjesecima živi u minusu = she has been living in the red for months already

This is an idiomatic expression.

Literally:

• živi = lives
• u minusu = in the minus

But financially it means something like:

• to be overdrawn
• to be in the red
• to be living with a negative bank balance
• to be constantly short of money / in debt

So živjeti u minusu is a common everyday way to talk about someone whose account or finances are below zero.

Yes, it is standard here.

The sentence begins with a subordinate clause:

Dok sam čekala u redu, ...

When that clause comes before the main clause, Croatian normally separates it with a comma.

So the punctuation is correct and expected.