Лодыжка всё ещё болела, и мне пришлось туго обмотать её бинтом.

Because лодыжка is the subject of болела. It is the thing that was hurting, so Russian uses the nominative.

You can also tell from the verb:

• лодыжка болела = the ankle hurt
• нога болела = the leg hurt

The noun лодыжка is feminine, singular, nominative.

In the past tense, Russian verbs agree with the subject in gender and number.

Since лодыжка is:

• singular
• feminine

the verb must be болела.

Compare:

• палец болел = the finger hurt
• лодыжка болела = the ankle hurt
• колено болело = the knee hurt
• ноги болели = the legs hurt

Всё ещё means still.

The combination emphasizes that the situation continued:

• ещё can mean still, yet, or more
• всё ещё specifically means still, continuing up to now / up to that point

So лодыжка всё ещё болела means the ankle had not stopped hurting.

A useful note: in normal printed Russian, всё is ideally written with ё, though many texts write е instead: все еще. In this sentence, the meaning is clearly всё ещё, not everyone yet.

This is a very common aspect pattern.

• болела is imperfective because it describes an ongoing state: the ankle was hurting.
• обмотать is perfective because it refers to a single necessary action with a result: wrapping it up.

So the sentence contrasts:

• an ongoing condition: it still hurt
• a completed response: I had to wrap it

If you used обматывать instead, it would sound more like focusing on the process, repetition, or an uncompleted action. After пришлось, Russian often prefers the perfective when talking about one concrete action.

Прийтись / приходиться is a very common Russian verb meaning to have to, to be forced to, or to end up having to.

The person who experiences the necessity goes in the dative:

• мне пришлось = I had to
• ему пришлось = he had to
• нам пришлось = we had to

So мне пришлось is not structured like English I had to. It is more like:

• to me, it fell/turned out necessary

That is why you see мне, not я.

Because this is an impersonal construction.

There is no real grammatical subject here, so Russian uses a default neuter past-tense form:

• пришлось

This happens in a number of Russian impersonal expressions.

So:

• мне пришлось уйти = I had to leave
• ей пришлось ждать = she had to wait

The form пришлось does not change for the gender of the person. It stays neuter because the construction itself is impersonal.

Because пришлось tells you that something was necessary, and the infinitive tells you what was necessary.

So:

• мне пришлось обмотать её бинтом = I had to wrap it with a bandage
• мне пришлось уйти = I had to leave
• нам пришлось ждать = we had to wait

This is the standard pattern:

• [dative person] + пришлось + infinitive

Туго is an adverb, and here it means tightly.

It modifies обмотать:

• туго обмотать = to wrap tightly

This word is often used when something is physically tight or snug:

• туго завязать = tie tightly
• туго затянуть = tighten firmly

So in this sentence, it describes how the bandage was wrapped.

Here её is the direct object pronoun, meaning her/it.

It refers back to лодыжка, so in English we would usually say it:

• обмотать её бинтом = wrap it with a bandage

You can tell it is not possessive because there is no noun after it. Compare:

• обмотать её бинтом = wrap it/her with a bandage
• её лодыжка = her ankle

So in this sentence, её is an object pronoun, not a possessive adjective.

Because бинт is the instrument or means used to do the action.

With обмотать, Russian commonly uses:

• обмотать кого-что чем
• wrap someone/something with something

So:

• её = direct object, what is being wrapped
• бинтом = instrumental, what you wrap it with

Compare:

• писать ручкой = write with a pen
• резать ножом = cut with a knife
• обмотать бинтом = wrap with a bandage

Yes. Russian word order is flexible, and this sentence uses a natural neutral order.

Current order:

• Лодыжка всё ещё болела, и мне пришлось туго обмотать её бинтом.

You could change the order for emphasis, for example:

• Лодыжка всё ещё болела, и мне пришлось её туго обмотать бинтом.
• Лодыжка всё ещё болела, и мне пришлось бинтом туго обмотать её.

These are grammatically possible, but they may sound less neutral or place emphasis in different spots.

The original version sounds smooth and normal:

• first the continuing pain
• then the necessary action
• then the method: tightly, with a bandage