У неї болить губа.

Because Ukrainian usually expresses who feels something with a prepositional phrase like у неї, not with the plain subject form вона.

• вона = she
• у неї = at her / in her / with her, but in this kind of sentence it functions like she has or for her

So:

• У неї болить губа. = Her lip hurts.
• Literally, it is closer to At her, the lip hurts.

This is a very common Ukrainian pattern for physical states:

• У мене болить голова. = My head hurts.
• У нього температура. = He has a fever.

Because губа is the grammatical subject of болить.

In Ukrainian, with body-part pain, the thing that hurts is often the subject:

• болить губа = the lip hurts
• болить рука = the arm hurts
• болять зуби = the teeth hurt

So губа stays in the nominative singular because it is the thing doing the grammatical hurting, even though in English we often think of the person as the main focus.

It is singular because губа is singular.

• губа = one lip
• therefore болить = singular hurts

Compare:

• У неї болить губа. = Her lip hurts.
• У неї болять губи. = Her lips hurt.

So the verb agrees with the body part, not with неї.

Боліти means to ache / to hurt / to be painful.

In this sentence, болить is the 3rd person singular present form:

• боліти = infinitive
• болить = hurts / is hurting / aches

Ukrainian often uses this verb in a structure where the painful body part is the subject:

• болить голова = my head hurts / the head hurts
• болять ноги = my legs hurt / the legs hurt

So it is very close to English hurts, but the sentence structure is often less personal and more body-part-centered.

Because Ukrainian does not need a possessive adjective here. The phrase у неї already tells you whose lip it is.

English often says:

• Her lip hurts

Ukrainian naturally says:

• У неї болить губа

Adding a possessive like її губа is possible in some contexts, but here it is usually unnecessary and can sound more emphatic or less natural.

So Ukrainian prefers the simpler pattern:

• у + person
• болить + body part

Yes. У and в are often interchangeable in Ukrainian.

Speakers choose у or в mostly for ease of pronunciation and sound flow. At the beginning of a sentence, У неї is very natural and common.

So both are possible:

• У неї болить губа.
• В неї болить губа.

Usually the choice is phonetic, not a difference in meaning.

The word order can change, because Ukrainian has relatively flexible word order.

The neutral order here is:

• У неї болить губа.

But you may also hear:

• Губа у неї болить.
• Болить у неї губа.

These versions can shift emphasis:

• У неї болить губа. = neutral
• Губа у неї болить. = emphasizing lip
• Болить у неї губа. = emphasizing the fact that it hurts

For learners, the original order is the safest default.

Because у requires a prepositional-case form, and the pronoun вона changes form.

Here are the relevant forms:

• вона = she
• неї = her, after certain prepositions such as у, в, до, біля

So:

• у неї = at her / with her
• до неї = to her
• біля неї = near her

This is a normal pronoun change, just like English changes she to her.

Неї is pronounced approximately ne-yi.

A helpful rough guide:

• не sounds like neh
• ї is pronounced like yi

So неї is roughly neh-yi, with two syllables.

Also remember:

• ї is always pronounced clearly as yi / ji
• it is not silent

So do not pronounce неї like one flat syllable. Keep both vowel parts audible.

Губа is singular: lip.

• губа = lip
• губи = lips

So this sentence means one lip hurts. If both lips hurt, Ukrainian would normally use the plural:

• У неї болять губи.

That is a good example of how the verb changes too:

• singular: болить
• plural: болять

Yes. That is a very natural English translation.

Depending on context, У неї болить губа can be understood as:

• Her lip hurts.
• She has a sore lip.
• Her lip is hurting.

The exact English wording can vary, but the Ukrainian structure stays the same.

Yes, very often. This is one of the most useful patterns to learn.

Examples:

• У мене болить голова. = My head hurts.
• У нього болить рука. = His arm hurts.
• У нас болять ноги. = Our legs hurt.
• У дитини болить живіт. = The child has a stomachache / The child’s stomach hurts.

So the pattern is:

• У + person
• болить / болять
• body part

Use болить with singular nouns and болять with plural nouns.

Yes, У неї болить губа is much more natural in everyday speech.

A phrase like вона має біль у губі is grammatical enough to be understood, but it sounds much less idiomatic and more formal, unnatural, or translated from another language.

For ordinary conversation, Ukrainians strongly prefer the боліти pattern:

• У неї болить губа.

So if you want to sound natural, this is the form to remember.