Ona cieszy się, kiedy córka wraca wcześniej ze szkoły.

Because cieszyć się is a reflexive verb in Polish, and it means to be happy / to rejoice / to be glad.

• cieszyć by itself usually means to please or to make someone happy
  • To mnie cieszy = That makes me happy
• cieszyć się means to feel happy
  • Ona cieszy się = She is happy / She is glad

So in this sentence, się is necessary because the meaning is about her emotional state, not about her making someone else happy.

In Polish, się is usually not placed at the very beginning of a clause, and it commonly comes after the verb.

So:

• Ona cieszy się = natural
• Ona się cieszy = also possible and natural
• Się ona cieszy = generally not normal in neutral speech

Both Ona cieszy się and Ona się cieszy can be correct, but the version in your sentence is a very standard word order.

Yes, it can be left out.

Polish often omits subject pronouns when the verb already makes the subject clear. So:

• Ona cieszy się, kiedy córka wraca wcześniej ze szkoły.
• Cieszy się, kiedy córka wraca wcześniej ze szkoły.

Both are correct.

Including ona can add a bit of emphasis or clarity, especially if you are contrasting her with someone else. English usually needs she, but Polish often does not.

Yes. In this sentence, kiedy means when, and it introduces a time clause.

You could also use:

• gdy = also when, often a little more formal or literary
• jak = sometimes used in colloquial Polish in time expressions, but it is less neutral here

So these are possible:

• Ona cieszy się, kiedy córka wraca wcześniej ze szkoły.
• Ona cieszy się, gdy córka wraca wcześniej ze szkoły.

For most learners, kiedy is the safest and most neutral choice.

In Polish, the present tense is often used for repeated, habitual, or general actions, just like in English.

So córka wraca wcześniej ze szkoły can mean:

• the daughter comes back earlier from school
• the daughter returns earlier from school
• when her daughter gets home early from school

It does not have to mean only right now. It can describe a general situation: whenever this happens, she is happy.

Because córka is the subject of the clause córka wraca wcześniej ze szkoły.

In Polish, the subject is typically in the nominative case. So:

• córka = nominative singular = daughter
• córkę = accusative singular, used when the daughter is the direct object

Here, the daughter is the one performing the action wraca (comes back), so nominative is required.

wcześniej usually means earlier.

It is the comparative adverb related to:

• wcześnie = early
• wcześniej = earlier

So wraca wcześniej ze szkoły means she comes back from school earlier—usually earlier than usual, earlier than expected, or earlier than some other time.

If you said wraca wcześnie, that would mean she comes back early in a more general sense.

Both z and ze mean from here, but ze is used for easier pronunciation in some combinations.

Because szkoły begins with a difficult consonant cluster after z, Polish uses ze:

• ze szkoły = from school

This is similar to how some languages slightly change a word for smoother pronunciation.

Also, z/ze in the sense of from requires the genitive case, which is why you get:

• szkoła → szkoły

Because after z/ze meaning from, Polish uses the genitive case.

So:

• szkoła = nominative = school
• ze szkoły = genitive = from school

This is a very common pattern in Polish:

• z domu = from the house/home
• z pracy = from work
• ze szkoły = from school

So the ending changes because the preposition controls the case.

Because kiedy córka wraca wcześniej ze szkoły is a subordinate clause.

In Polish, subordinate clauses are normally separated by a comma, especially when introduced by words like:

• kiedy = when
• że = that
• bo = because
• jeśli = if
• gdy = when

So the comma in:

• Ona cieszy się, kiedy córka wraca wcześniej ze szkoły.

is standard and expected.

Yes, Polish word order is more flexible than English, although different orders can sound more neutral, more emphatic, or more literary.

Neutral version:

• Ona cieszy się, kiedy córka wraca wcześniej ze szkoły.

Other possible versions:

• Kiedy córka wraca wcześniej ze szkoły, ona cieszy się.
• Ona się cieszy, kiedy córka wraca wcześniej ze szkoły.
• Cieszy się, kiedy córka wraca wcześniej ze szkoły.

These all mean roughly the same thing, but the original sentence is a very natural, standard way to say it.

By itself, it most naturally sounds like a general or repeated situation:

• She is happy when her daughter comes home early from school

That is because both verbs are in the present tense, which often expresses a regular pattern.

If you wanted to make it clearly about one specific past occasion, Polish would normally use past forms, for example:

• Ona ucieszyła się, kiedy córka wróciła wcześniej ze szkoły.

So the original sentence most naturally suggests whenever this happens or in that kind of situation.