Она вернулась спустя неделю.

Because the basic verb here is вернуться, not вернуть.

• вернуться = to return, to come back
• вернуть = to return something, to give something back

So:

• Она вернулась = she came back / she returned
• Она вернула книгу = she returned the book

The -сь / -ся ending is part of the verb and changes the meaning. In this sentence, she herself came back; she did not return an object.

Here -сь is the reflexive marker, a shorter form of -ся used after a vowel.

In this sentence, it does not mean herself in a literal English sense. Instead, it is simply part of the verb вернуться.

A useful way to think about it:

• вернуть = to return something
• вернуться = to return oneself / to come back

So -сь helps make the verb intransitive: the action happens to the subject rather than to an object.

That is the past tense marker for a feminine singular subject.

Russian past tense agrees with gender and number:

• вернулся = he returned
• вернулась = she returned
• вернулось = it returned
• вернулись = they returned

Since она is feminine singular, the correct form is вернулась.

Вернулась is perfective.

The verb pair is:

• возвращаться / возвращаться or вернуться/возвращаться depending on style and meaning
• here the key pair is возвращаться (imperfective) / вернуться (perfective)

In this sentence, the perfective is used because the return is seen as a completed event: she was away, and then she came back.

Compare:

• Она возвращалась = she was returning / she used to return
• Она вернулась = she returned / came back

The sentence describes one finished action, so perfective is natural.

Спустя means after or later, especially when talking about a period of time that has passed.

So спустя неделю means:

• after a week
• a week later

It often appears in narrative language and is very common in both speech and writing.

Examples:

• Спустя час он позвонил. = An hour later, he called.
• Спустя много лет они встретились снова. = Many years later, they met again.

Because спустя is followed by the accusative case, and the accusative singular of неделя is неделю.

Declension:

• nominative: неделя
• accusative: неделю

So:

• спустя неделю
• спустя минуту
• спустя месяц
• спустя год

This is one of the main grammar points in the sentence: спустя + accusative.

Yes, very often you can.

• Она вернулась спустя неделю.
• Она вернулась через неделю.

Both can mean She returned after a week / a week later.

However, there is a slight tendency:

• через неделю often sounds like a straightforward time expression: in a week / after a week
• спустя неделю can sound a little more narrative or literary: a week later

In many everyday contexts, both are fine.

Yes. Russian word order is flexible.

These are all possible:

• Она вернулась спустя неделю.
• Спустя неделю она вернулась.
• Она спустя неделю вернулась.

The meaning stays basically the same, but the emphasis changes.

• Она вернулась спустя неделю. = neutral
• Спустя неделю она вернулась. = emphasizes the time frame, after a week
• Она спустя неделю вернулась. = also possible, often with spoken emphasis

Russian often uses word order to highlight what is new, important, or contrasted.

It can be omitted if the context already makes it clear who is being talked about.

So you may hear:

• Вернулась спустя неделю. = Returned after a week / She came back after a week

Russian often drops subjects when they are understood from context.

One thing to remember: in the past tense, the verb shows gender and number, but not person as clearly as present-tense forms do. So вернулась tells you the subject is feminine singular, but not explicitly she unless the context makes that obvious.

It can be either, depending on context.

• returned is a direct, dictionary-style translation
• came back is often more natural in everyday English

Russian вернуться comfortably covers both ideas. So when learning the sentence, it is best to connect вернуться with the general idea of coming back / returning.

The stress is:

• Она́
• верну́лась
• спустя́
• неде́лю

A rough pronunciation guide:

• Она́ ≈ a-NA
• верну́лась ≈ veer-NU-las’
• спустя́ ≈ spus-TYA
• неде́лю ≈ nee-DYE-lyu

A few notes:

• unstressed о in она sounds more like a
• the final -сь is soft
• лю in неделю is pronounced with a lyu sound

Yes. Неделю спустя is also very common.

So you can say:

• Она вернулась спустя неделю.
• Она вернулась неделю спустя.

Both mean essentially the same thing.

A slight nuance:

• спустя неделю is the more straightforward preposition + noun pattern
• неделю спустя is a very common time expression and may sound a bit more idiomatic in some contexts

Both are natural Russian.

The dictionary form is вернуться.

When you look up verbs in Russian, you usually need the infinitive. From вернулась, you can work backward like this:

• past tense feminine singular ending: -лась
• base infinitive: вернуться

So if you want to find this verb in a dictionary or vocabulary list, search for вернуться.