Ella liberó la presión despacio.

Yes. Spanish often drops subject pronouns when the verb already makes the subject clear.

• Liberó la presión despacio = She released the pressure slowly
• Ella liberó la presión despacio adds emphasis or contrast

You might use ella if you want to stress she as opposed to someone else:

• Él no lo hizo. Ella liberó la presión despacio.

So ella is grammatically optional here, but not wrong.

Liberó is the preterite form of liberar, for él/ella/usted. It tells you the action is seen as a completed event in the past.

• libera = she releases / is releasing depending on context
• liberaba = she was releasing / used to release
• liberó = she released

So liberó suggests a finished action: she released it, and that action is treated as complete.

The accent mark shows both pronunciation and helps distinguish forms.

• libero without an accent could be read differently and is not the same verb form here
• liberó stresses the last syllable: li-be-RÓ

This is the third-person singular preterite ending for many -ar verbs:

• habló
• caminó
• liberó

So the accent is an important part of the spelling.

Presión is a feminine noun, so it takes la in the singular:

• la presión
• una presión

In this sentence, la usually means a specific pressure already understood from context, not just pressure in general.

Examples:

• Liberó la presión = released the pressure
• Liberó presión would sound less natural in many contexts unless you mean something more general or technical

So la presión is the normal way to say the pressure.

Yes, liberar can work, especially in technical or physical contexts, but Spanish may also use other verbs depending on what kind of pressure is meant.

Common alternatives:

• soltar la presión = let out the pressure
• aliviar la presión = relieve the pressure
• reducir la presión = reduce the pressure

If this is about a machine, valve, tyre, or container, liberar la presión sounds quite possible. In other situations, another verb may sound more natural.

Both can mean slowly, but they are not always identical in tone.

• despacio is very common and natural in everyday speech
• lentamente is also correct, but can sound a bit more formal or descriptive

So:

• Ella liberó la presión despacio = very natural
• Ella liberó la presión lentamente = also correct

In many everyday sentences, learners will hear despacio more often.

Yes. Spanish adverbs often have flexible position.

All of these are possible:

• Ella liberó la presión despacio.
• Ella despacio liberó la presión.
• Despacio, ella liberó la presión.

The most natural neutral version here is usually:

• Ella liberó la presión despacio.

Putting despacio first can emphasize the manner:

• Despacio, ella liberó la presión.

So the original word order is natural, but not the only option.

Here it is an adverb, because it describes how she released the pressure.

It modifies the verb liberó:

• She released it slowly

Compare:

• un movimiento despacio ❌ not correct
• un movimiento lento ✅ adjective
• se movió despacio ✅ adverb

So despacio is functioning as an adverb of manner.

A simple guide:

• ella: EH-ya in most of Spain, though pronunciation varies by region
• liberó: lee-beh-RO
• la presión: la preh-SYON
• despacio: des-PA-thyo in most of Spain, or des-PA-syo in seseo pronunciation

A few key points for Spain:

• ll is often pronounced like y
• ci in despacio is often like English th in much of Spain
• the final stress in liberó and presión is important

Grammatically, yes, but in natural English liberated the pressure often sounds odd. English usually prefers something like:

• released the pressure slowly
• let the pressure out slowly

This is useful for learners because Spanish liberar often corresponds to English release, not always liberate.

So when learning vocabulary, it is better to think in terms of how the word is actually used, not only its closest-looking English relative.

Because la presión is the direct object of liberó.

She did the action directly to the pressure:

• liberó la presión

No preposition is needed.

Compare with a sentence that does need a preposition:

• Habló de la presión = She spoke about the pressure

Here, though, la presión receives the action directly, so there is no a, de, or other preposition.

It could be similar, but not always exactly the same.

• soltar often means to let go, let out, or release
• liberar can sound a bit more technical or formal depending on context

If you are talking about letting pressure out of a system, soltó la presión may sound very natural in some contexts. But the best choice depends on the situation.

So they can overlap, but they are not perfect substitutes in every sentence.