Po kilku latach pracy została architektką, choć wcześniej była pielęgniarką.

Polish often drops subject pronouns when they are clear from the verb form.

Here, both została and była are feminine singular past tense forms, so a Polish speaker immediately understands that the subject is she.

So Polish says:

• została = she became
• była = she was

Adding ona would usually be unnecessary unless you want extra emphasis.

In the past tense, Polish verbs show gender in the singular.

• została = feminine singular
• była = feminine singular

If the subject were masculine, you would get:

• został
• był

So the sentence clearly refers to a woman.

Here została is the past tense of zostać, and it means became.

So:

• została architektką = she became an architect

Be careful: zostać can also mean to stay, to remain, or to be left, depending on context. But with a profession or role, it very often means to become.

Because after zostać and usually after być when talking about someone's profession, role, or identity, Polish commonly uses the instrumental case.

So:

• architektka → architektką
• pielęgniarka → pielęgniarką

This is why the sentence says:

• została architektką
• była pielęgniarką

For English speakers, this is one of the big differences from English: Polish changes the noun form after verbs like to be and to become.

Because the sentence refers to a woman, and Polish uses the feminine noun architektka.

Its cases are:

• nominative: architektka
• instrumental: architektką

So after została, the correct form is architektką.

You may sometimes see women referred to with masculine profession nouns in some contexts, but here the sentence uses the regular feminine form.

This phrase contains a few case changes:

• po takes the locative
• kilka becomes kilku
• lata becomes latach

So:

• po kilku latach = after several years

Then pracy is the form of praca used in the expression lata pracy = years of work / years of working.

So the whole phrase means:

• po kilku latach pracy = after several years of work

Because the preposition po requires the locative case.

Compare:

• kilka lat = several years
• po kilku latach = after several years

So lat is not wrong in general; it is just used in a different grammatical environment. After po, you need latach.

Pracy is from praca, meaning work.

Here it means something like:

• years of work
• years of working
• years spent working

It does not necessarily specify what job she was doing during those years. The sentence only tells us that earlier she was a nurse, and later she became an architect.

Choć means though, although, or even though.

Yes, chociaż is very close in meaning and often interchangeable.

So these are both natural:

• ..., choć wcześniej była pielęgniarką.
• ..., chociaż wcześniej była pielęgniarką.

Choć is a bit shorter and sometimes slightly more compact in style, but both are common.

Because choć introduces a subordinate clause.

Polish punctuation normally uses a comma before conjunctions like:

• choć
• że
• bo
• ponieważ
• który

So the comma in:

• została architektką, choć wcześniej była pielęgniarką

is standard and necessary.

Modern Polish usually does not use a separate pluperfect form in ordinary speech the way English does.

Instead, Polish normally uses:

• the ordinary past tense
• plus a time word such as wcześniej = earlier / previously

So:

• wcześniej była pielęgniarką

naturally means:

• earlier she was a nurse
• or in good English, she had previously been a nurse

In other words, Polish often lets the time relationship come from context or from adverbs like wcześniej.

Wcześniej means earlier, previously, or before that.

It tells you that being a nurse happened before becoming an architect.

So:

• choć wcześniej była pielęgniarką = although earlier she was a nurse / although she had previously been a nurse

It helps show the contrast in her career path.

Not completely. Polish word order is fairly flexible, although some versions sound more natural than others.

This sentence is very natural as written:

• Po kilku latach pracy została architektką, choć wcześniej była pielęgniarką.

But you could also move parts for emphasis, for example:

• Wcześniej była pielęgniarką, ale po kilku latach pracy została architektką.

That version shifts the focus slightly by starting with her earlier profession.

So the original word order is natural, but not the only possibility.