Рана неглубокая, но её всё равно нужно промыть водой.

Because неглубокая agrees with рана, and рана is:

• feminine
• singular
• nominative

So the adjective must also be feminine singular nominative:

• рана — wound
• неглубокая — not deep / shallow

This is basic adjective agreement in Russian.

In Russian, the verb to be is usually omitted in the present tense.

So:

• Рана неглубокая literally looks like The wound not-deep
• but it means The wound is not deep

This is completely normal in Russian.
If you wanted the past or future, you would use forms of быть:

• Рана была неглубокая — The wound was not deep
• Рана будет неглубокая — The wound will be not deep

Written together, неглубокая usually means a straightforward quality: shallow / not deep.

Written separately, не глубокая often sounds more contrastive or emphatic, as if you are denying deep specifically:

• рана неглубокая — the wound is shallow
• рана не глубокая, а поверхностная — the wound is not deep, but superficial

In your sentence, неглубокая is the natural choice.

Because её is the object form of она.

Here рана is being referred to as it/her, and it is the direct object of промыть:

• она — she / it
• её — her / it

So:

• её нужно промыть — it needs to be rinsed

You cannot use она here, because она is the subject form.

Yes, but Russian nouns have grammatical gender, and рана is feminine.
So when you replace рана with a pronoun, Russian uses the feminine form:

• рана → она / её

In English we usually say it for objects and body parts, but Russian follows grammatical gender, not natural gender.

So её here means it, referring to the wound.

Всё равно here means all the same, anyway, or still.

So:

• но её всё равно нужно промыть водой
  = but it still needs to be rinsed with water = but you should rinse it with water anyway

It adds the idea that even though the wound is not deep, the action is still necessary.

A very common learner mistake is to think всё равно always means emotional indifference like I don’t care. It can mean that in other contexts, but here it means nevertheless / anyway.

This is an impersonal construction.

• нужно = it is necessary / one must / needs to
• промыть = to rinse, to wash out

So её нужно промыть literally means:

• it is necessary to rinse it

In natural English, we usually say:

• it needs to be rinsed
• you should rinse it

Russian often uses нужно + infinitive when the speaker is talking about what is necessary, without naming who must do it.

Yes. In this sentence, надо and нужно are both possible:

• её всё равно нужно промыть водой
• её всё равно надо промыть водой

Both mean roughly the same thing: it still needs to be rinsed with water.

Very broadly:

• нужно can sound a little more neutral or formal
• надо can sound a little more conversational

But in everyday speech, both are very common.

Because промыть is the perfective verb, and it fits a single completed action.

Compare:

• мыть — to wash
• промывать — to rinse / wash through, imperfective
• промыть — to rinse / wash through, perfective

Here the sentence is about one necessary action to do to the wound, so perfective промыть is natural:

• нужно промыть — it needs to be rinsed

If you used промывать, it would sound more like repeated or ongoing action, or general procedure in some contexts.

In промыть, the prefix про- gives the idea of washing/rinsing something through or properly.

So промыть рану is not just wash a wound in a vague sense. It is more specifically:

• rinse the wound
• clean it out with liquid

That is why промыть is very natural in a medical or first-aid context.

Because водой is the instrumental case of вода.

After verbs like промыть, Russian often uses the instrumental to show the substance or means used:

• промыть водой — rinse with water
• резать ножом — cut with a knife
• писать ручкой — write with a pen

So:

• вода — water
• водой — with water

This is a very common use of the instrumental case.

Yes, absolutely.

Full version:

• Рана неглубокая, но рану всё равно нужно промыть водой.

But Russian often avoids repeating the noun and uses a pronoun instead:

• Рана неглубокая, но её всё равно нужно промыть водой.

That sounds more natural.

Yes, Russian word order is flexible.

This sentence uses a very natural neutral order:

• её всё равно нужно промыть водой

But other orders are possible, depending on emphasis:

• её нужно всё равно промыть водой
• всё равно её нужно промыть водой
• промыть её всё равно нужно водой
  (possible, but less neutral)

The usual idea is:

• её introduces what we are talking about
• всё равно highlights anyway / still
• нужно промыть gives the necessity
• водой comes naturally at the end as the means

So the original order is a good standard model.

It sounds like normal, standard Russian and would be completely natural in everyday speech, medical advice, or first-aid instructions.

It is not overly formal, and it is not slangy either.
A doctor, parent, nurse, or first-aid guide could all say something like this.

A very natural conversational variant would be:

• Рана неглубокая, но её всё равно надо промыть водой.

Using надо instead of нужно makes it feel a bit more informal and spoken.

Another conversational option is:

• Рана неглубокая, но всё равно промой её водой.

That changes the structure to the imperative:

• промой — rinse it

This sounds more direct, like advice or instruction to a specific person.

Yes, ё is pronounced yo, so её is pronounced roughly ye-YO.

A few useful points:

• её has two syllables
• the stress is on the final ё
• you should not pronounce it like a single English yo

So it is approximately:

• е-йо

Also, in printed Russian, ё is sometimes written as е, but the word is still understood as её.

Sometimes in context, yes, but literally it means a wound that is not deep.

English often broadens this idea into minor, but Russian is being more specific here: the depth is not serious.

So the most direct meaning is:

• a shallow wound
• a wound that isn’t deep

Whether it is truly minor depends on context. A wound can be not deep and still need cleaning, which is exactly the point of the sentence.