Сегодня у неё был ровный пробор, а завтра она хочет снова заплести косу.

In Russian, possession is very often expressed with у + genitive plus есть / был / будет.

So:

• у неё был пробор literally means at her there was a parting
• natural English translation: she had a parting

Russian usually avoids иметь in everyday situations like this unless the meaning is more formal, emphatic, or abstract.

A few similar examples:

• У меня есть машина. = I have a car.
• У него был брат. = He had a brother.
• У неё будет новая причёска. = She will have a new hairstyle.

So у неё был ровный пробор is the normal, natural way to say she had a straight/even parting.

Because the preposition у requires the genitive case.

The pronoun она changes by case:

• nominative: она = she
• genitive: её / неё = of her / at her / her

After many prepositions, Russian uses the form неё instead of её. So:

• у неё = at her / she has
• для неё = for her
• без неё = without her

This is just a standard pronoun form after a preposition.

Because in the past tense, Russian verbs agree with the grammatical subject, not with the possessor.

In this part of the sentence, the grammatical subject is пробор:

• пробор = masculine noun
• therefore: был

So the structure is:

• у неё = with her / she had
• пробор = the thing that existed
• был agrees with пробор

That is why it is:

• У неё был пробор.

Compare:

• У неё была коса. — because коса is feminine
• У неё было короткое каре. — because каре is neuter
• У неё были длинные волосы. — because волосы is plural

Because adjectives must agree with the noun they describe in gender, number, and case.

Here:

• пробор is masculine singular nominative
• so the adjective must also be masculine singular nominative
• therefore: ровный пробор

Agreement pattern:

• masculine: ровный пробор
• feminine: ровная коса
• neuter: ровное каре
• plural: ровные линии

So ровная пробор would be grammatically incorrect.

Пробор is the line made in the hair when it is parted.

In English, depending on context, it can be translated as:

• part
• parting
• hair part

So ровный пробор means something like:

• a straight part
• a neat/even parting

The adjective ровный literally means even, smooth, straight, neat, and here it suggests that the hair part was tidy and straight.

А can sometimes be translated as and, but very often it introduces a contrast or switch of focus.

Here the sentence contrasts:

• Сегодня... = Today...
• а завтра... = but tomorrow / and tomorrow, by contrast...

So in this sentence, а is doing more than simple joining. It sets up a contrast between two situations:

• today she had one hairstyle
• tomorrow she wants a different one again

A natural sense in English would be:

• Today she had a straight parting, but tomorrow she wants to braid her hair again.

So yes, а can be translated as and in some contexts, but here but / whereas / while captures the contrast better.

In the first part, Russian uses the possession structure у неё был..., so the idea of she is already contained inside у неё.

In the second part, the structure changes: now она is the grammatical subject of хочет.

Compare the two parts:

• Сегодня у неё был ровный пробор
  Literally: Today, at her there was a straight parting
• а завтра она хочет снова заплести косу
  Literally: but tomorrow she wants to braid a braid/plait again

So она appears because хочет needs a subject, and here that subject is directly она.

Russian often changes structure like this naturally, even inside the same sentence.

Because коса is the direct object of the infinitive заплести, so it goes into the accusative case.

For this noun:

• nominative: коса
• accusative: косу

So:

• заплести косу = to braid a braid / to plait the hair into a braid

This is normal for feminine nouns ending in -а:

• читать книгу — to read a book
• видеть сестру — to see a sister
• заплести косу — to braid a plait

Russian коса has more than one meaning, including:

• braid / plait (of hair)
• scythe
• sometimes sandspit in geography

Here, because the sentence is about hairstyle, коса clearly means:

• braid
• plait

So заплести косу means to braid one’s hair into a braid or simply to make a braid.

This is an aspect question.

• плести = imperfective
• заплести = perfective

Very roughly:

• плести focuses on the process: to be braiding / to braid
• заплести focuses on the completed result: to braid up / to finish making a braid

In this sentence, she wants to achieve the result of having a braid tomorrow, so заплести is very natural.

After хотеть, Russian can use either imperfective or perfective infinitives, depending on the meaning:

• хочет плести = wants to be braiding / wants to braid as an activity
• хочет заплести косу = wants to braid her hair into a braid, with the finished result in mind

So the perfective here makes excellent sense.

Снова means again.

So снова заплести косу means:

• to braid her hair again
• to make a braid again

It suggests that this is not the first time. Maybe she used to wear a braid before, or she had one recently, and now she wants to return to that hairstyle.

Russian also has опять, which often also means again. In many contexts, снова and опять overlap, though опять can sometimes sound a little more conversational or carry extra emotional color depending on tone.

Yes, Russian word order is relatively flexible, but different orders change the emphasis.

This version is very natural:

• а завтра она хочет снова заплести косу

It presents the time first:

• завтра = tomorrow

Then the subject:

• она = she

Then the verb phrase:

• хочет снова заплести косу = wants to braid her hair again

Other word orders are possible, for example:

• А она завтра хочет снова заплести косу.
• А завтра хочет она снова заплести косу.
• А завтра она снова хочет заплести косу.

These are not all equally neutral. The original version is the most straightforward and natural for ordinary narration.

In general, Russian often puts time expressions like сегодня and завтра near the beginning when setting the scene.

Yes. The sentence contrasts:

• a situation today: Сегодня у неё был ровный пробор
• a plan/desire for tomorrow: а завтра она хочет...

Russian often uses хотеть + infinitive to talk about what someone wants to do in the future.

So instead of saying something like tomorrow she will braid her hair again, the sentence says:

• tomorrow she wants to braid her hair again

That focuses on intention or desire, not just a future fact.

So the time words and verb forms work together like this:

• сегодня + past = what was true today
• завтра + wants to + infinitive = what she intends for tomorrow