Она попросила об одолжении.

О and об are two forms of the same preposition, meaning about/regarding in this kind of construction.

Russian uses об before words that begin with a vowel, mainly for ease of pronunciation:

• о брате
• об отце
• об одолжении

So об одолжении is used because одолжении starts with о.

You may also see обо in a few fixed or traditional combinations, such as обо мне.

Because after о / об, Russian normally uses the prepositional case.

The dictionary form is одолжение, but in the prepositional singular it becomes одолжении:

• одолжение → nominative
• об одолжении → prepositional

This happens because nouns ending in -ие usually change to -ии in the prepositional singular:

• здание → в здании
• сомнение → в сомнении
• одолжение → об одолжении

So this is a normal case change, not an irregular phrase you just have to memorize.

Попросила is the perfective past tense form of попросить.

That means the sentence presents the request as a completed single event: she made the request.

Compare:

• Она попросила об одолжении. = She asked for a favor.
  → one completed request

• Она просила об одолжении. = She was asking for a favor / She asked for a favor
  → more emphasis on the process, repetition, or ongoing action

So in a simple statement about one finished action, попросила is very natural.

In the Russian past tense, verbs show gender and number.

So:

• попросил = masculine
• попросила = feminine
• попросило = neuter
• попросили = plural

Because the subject is она, the verb must be feminine: попросила.

This is one thing that feels very different from English, where past tense verbs do not change for gender.

It can be omitted if the context already makes the subject clear.

However, in the past tense, Russian verbs do not show person, only gender and number. So попросила by itself could mean:

• I asked (if the speaker is female)
• you asked (to a woman, in context)
• she asked

Because of that, adding она makes the subject clear.

So:

• Она попросила об одолжении. = clear on its own
• Попросила об одолжении. = possible in context, but less clear by itself

Russian can leave that out if it is obvious or not important.

The sentence only tells us that she asked for a favor, not whom she asked.

If you want to include the person, you can:

• Она попросила меня об одолжении. = She asked me for a favor.
• Она попросила его об одолжении. = She asked him for a favor.

So the omitted person is not a grammar problem; it is simply information the sentence does not include.

This is a very common point of confusion.

• спросить = to ask a question
• попросить = to ask for something / request something

So:

• Она спросила меня о времени. = She asked me about the time.
• Она попросила меня о помощи. = She asked me for help.

In your sentence, she is making a request, so попросила is the correct verb.

The natural pattern is попросить об одолжении or попросить кого-то об одолжении.

So these are good:

• Она попросила об одолжении.
• Она попросила меня об одолжении.

Saying попросила одолжение is not the normal construction.

A related expression is:

• сделать одолжение = to do someone a favor

For example:

• Сделай мне одолжение. = Do me a favor.

So it is useful to remember одолжение together with these common verb patterns.

No, Russian word order is fairly flexible, but the version you have is the most neutral.

• Она попросила об одолжении. = neutral, standard order

Other orders are possible for emphasis:

• Об одолжении она попросила вчера.
• Она вчера попросила об одолжении.

Changing the order changes the focus, not the basic meaning.

One thing that usually stays together is the preposition plus noun:

• об одолжении

You normally would not split those apart.

It mainly means favor in this sentence.

But yes, it is historically and semantically connected with the idea of lending or obliging someone. That is why learners sometimes notice a connection with the verb одолжить.

In modern usage, though, попросить об одолжении is understood simply as to ask for a favor.

So for this sentence, the safest way to think of одолжение is just:

одолжение = favor

The stress is:

Она́ попроси́ла об одолже́нии.

A rough pronunciation guide:

• Она́ = a-NA
• попроси́ла = pa-pra-SEE-la
• об одолже́нии = ab a-dal-ZHÉ-ni-i

The preposition об is unstressed and closely attached to the following word.

For listening and speaking, the most important stresses to remember are:

• попроси́ла
• одолже́нии