Она уехала надолго.

Уехала is past tense. In Russian, past tense verbs agree with gender and number:

• уехал = he left / went away
• уехала = she left / went away
• уехало = it left / went away
• уехали = they left / went away

So the final -а shows that the subject is feminine: она.

Because уехала and ехала do not mean the same thing.

• ехать / ехала describes the process of going by transport: she was going / she went (was traveling)
• уехать / уехала means to leave / to go away, focusing on departure and the result that the person is now gone

So Она уехала надолго is about the fact that she left and will be away for a long time, not about her being in the middle of traveling.

The prefix у- often gives the idea of going away, departing, or moving off from a place.

So:

• ехать = to go / travel by vehicle
• уехать = to leave, to go away, to depart by vehicle

It usually implies that the person has left the place where the speaker is mentally located.

Because уехать is a perfective verb. Perfective verbs present an action as a whole or as completed.

Here that matters because the sentence is about a finished event: she has left / left, and now the result is relevant — she will be away for a long time.

The imperfective partner is уезжать:

• Она уезжала = she was leaving / used to leave / left on some occasion (viewed as process or background)
• Она уехала = she left (completed, result-focused)

Надолго is an adverb meaning for a long time.

It is not a noun phrase like на долгий срок in this sentence. It behaves as one word and modifies the verb:

• уехала надолго = left for a long time

A useful contrast is:

• надолго = for a long time
• ненадолго = for a short time / not for long

Because in modern Russian надолго is a fixed adverb, so it is written as one word.

Russian has a number of adverbs formed historically from combinations like this, and learners often just need to memorize them as single adverbs:

• надолго = for a long time
• ненадолго = not for long

Writing на долго would normally be considered incorrect in this meaning.

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

For example:

• Уехала надолго. = She left for a long time.

Russian often drops subjects when they are understood from context. However, она may be kept for clarity, contrast, or emphasis.

Originally, yes: ехать / уехать is the verb family for going by transport. So in a strict sense, уехала suggests leaving by some vehicle.

Compare:

• уйти = to leave on foot
• уехать = to leave by vehicle
• улететь = to leave by flying
• уплыть = to leave by sailing/swimming

In everyday speech, though, уехать is very commonly used when someone has gone away to another city, country, etc., and the exact mode of travel may not matter much.

Yes. Russian word order is flexible, and changing it can shift emphasis.

For example:

• Она уехала надолго. = neutral statement
• Надолго она уехала. = stronger emphasis on for a long time
• Уехала она надолго. = can sound more contrastive or expressive, depending on context

The basic meaning stays the same, but the information focus changes.

Yes. Она уехала на долгое время is grammatical and means roughly the same thing.

But надолго is:

• shorter
• more natural in everyday speech
• very common

So Она уехала надолго is usually the more idiomatic choice.

The standard stress is:

• онá
• уéхала
• надóлго

So the whole sentence is pronounced approximately as:

онá уéхала надóлго

Stress is important in Russian, because it is not always predictable from spelling.