En días de tristeza, mi abuela prefiere pasear un rato y tomar el aire.

En días de tristeza is a natural, slightly general way to mean on sad days, in times of sadness, or when she feels sad.

Why there is no los:

• Without the article, Spanish often sounds more general.
• En días de tristeza refers to that kind of day in general, not a specific set of days already identified.

Compare:

• En días de tristeza = on sad days / in times of sadness
• En los días de tristeza = on the sad days, possibly referring to specific days already known in the context

So the version in the sentence sounds broad and idiomatic.

Tristeza is a noun meaning sadness.

So:

• días de tristeza literally means days of sadness
• It is a noun phrase, not an adjective phrase

A different option would be:

• días tristes = sad days

Both can work, but they feel slightly different:

• días de tristeza sounds a bit more literary or emotional
• días tristes is more direct and simple

Mi abuela means my grandmother and is the normal way to identify whose grandmother you mean.

Spanish often uses possessives like mi, tu, su just as English does.

Compare:

• mi abuela = my grandmother
• la abuela = the grandmother / grandmother, when the person is already clear from context
• abuela by itself is usually used when directly addressing her, like Abuela, ven aquí

So in this sentence, mi abuela is the most straightforward choice.

Prefiere is the third-person singular present form of preferir.

Here it means:

• mi abuela prefiere... = my grandmother prefers...

The structure is:

• preferir + infinitive
• preferir + noun

Examples:

• Prefiere pasear. = She prefers to go for a walk.
• Prefiere el té. = She prefers tea.

In your sentence:

• prefiere pasear un rato y tomar el aire

So she prefers to walk for a while and get some air.

All of these can exist, but they are not exactly the same in use.

pasear

Here it means to go for a walk. This is completely natural.

pasearse

This can also mean to walk around / stroll around, but sometimes it adds a nuance of moving around a place, or even showing oneself around, depending on context.

dar un paseo

This is another very common expression meaning to take a walk.

So these are all possible, but:

• prefiere pasear un rato is simple and natural
• prefiere dar un paseo would also be very common

Un rato means a while or for a bit.

It is a very common time expression.

Examples:

• Voy a descansar un rato. = I’m going to rest for a while.
• Hablamos un rato. = We talked for a while.

In the sentence:

• pasear un rato = to walk for a while

It suggests a short, indefinite amount of time.

Because un rato is being used as a duration expression, and Spanish often uses these directly without a preposition.

So:

• pasear un rato = walk for a while
• esperar una hora = wait for an hour
• dormir toda la noche = sleep all night

English often needs for, but Spanish often does not.

Tomar el aire is an idiomatic expression. It does not usually mean literally to take the air.

It means something like:

• to get some air
• to get some fresh air
• to go outside for air

In this sentence, it suggests that going out and breathing fresh air helps when she feels sad.

It is a common, natural expression in Spanish.

Because tomar el aire is a fixed expression. Spanish often uses el aire idiomatically here.

So:

• tomar el aire = get some air / get some fresh air

You can also say:

• tomar el aire fresco
• salir a tomar el aire

But tomar el aire by itself is already complete and idiomatic.

Because Spanish, like English, can use one main verb with multiple infinitives joined by y.

So:

• prefiere pasear un rato y tomar el aire

means:

• she prefers to walk for a while and get some air

The verb prefiere governs both infinitives:

• pasear
• tomar

This is completely normal.

Normally, y is the clearest and most natural option when linking the two actions.

• pasear un rato y tomar el aire = walk for a while and get some air

Without y, the sentence would sound less standard unless the style were more literary or elliptical. In everyday Spanish, keeping y is best.

It is understandable and natural, but it sounds a little more thoughtful or literary than casual everyday speech.

A person might also say:

• Cuando está triste... = When she is sad...
• En los días en que está triste... = On the days when she feels sad...
• Cuando se siente triste... = When she feels sad...

So the original phrase is fine, but it has a slightly more elegant tone.

The comma separates the introductory phrase from the main clause.

So the structure is:

• En días de tristeza, = introductory time/circumstance phrase
• mi abuela prefiere... = main clause

This comma is helpful and natural in writing, especially because the opening phrase sets the scene before the main statement.

Yes, grammatically it could:

• mi abuela prefiere tomar el aire y pasear un rato

That is possible, but the original order feels natural because:

1. first she goes for a walk
2. and as part of that, she gets some air

So the original sequence sounds smooth and logical.

Good question. Pasear can be used in different ways.

Intransitive use

• pasear = to go for a walk / to stroll

Example:

• Mi abuela pasea.

Transitive use

• pasear al perro = to walk the dog

In your sentence:

• prefiere pasear un rato

Here pasear is being used intransitively, meaning to go for a walk.
The phrase un rato is not a direct object; it expresses duration.

Yes, the sentence is natural and understandable in Spain.

Especially Spanish-sounding elements include:

• pasear un rato
• tomar el aire

A very everyday alternative in Spain might also be:

• Cuando está triste, mi abuela prefiere dar un paseo y tomar el aire.

But your original sentence sounds perfectly good.