Cuando ve el columpio libre, sonríe como si ya supiera que le toca a ella.

Because ver and mirar are not exactly the same.

• ver = to see, to notice
• mirar = to look at, to watch

Here, the idea is that she notices that the swing is free, so ve is the natural choice.
If you said mira el columpio libre, it would sound more like she is actively looking at the free swing.

This sentence is written in the present to describe the scene as if it is happening now, or as part of a narrative style.

So:

• Cuando ve el columpio libre, sonríe... = When she sees the swing free/available, she smiles...

Spanish often uses the present like this in descriptions and storytelling.

If the whole sentence were in the past, you would probably get:

• Cuando vio el columpio libre, sonrió...

In Spanish, adjectives usually come after the noun.

So:

• el columpio libre = the free/available swing

With libre, putting it after the noun sounds normal and describes the swing’s current state: it is unoccupied or available.

Putting libre before the noun would sound unusual here and could feel literary or change the nuance.

Here, libre means free, available, or unoccupied.

In this context, it does not mean politically free or free in an abstract sense. It means nobody is using the swing.

A very common playground-type phrase is:

• Hay un columpio libre = There is a free swing

In Spain, columpio normally means swing in a playground.

So here it refers to the seat hanging from chains or ropes that a child uses in a park.

The accent mark shows that the í is stressed.

• sonríe

It helps indicate the correct pronunciation and prevents the vowels from being read as a single diphthong.
A learner can think of it roughly as:

• son-rí-e

It comes from the verb sonreír = to smile.

Because como si normally requires the imperfect subjunctive in standard Spanish.

So:

• como si ya supiera = as if she already knew

This structure expresses something imagined, apparent, or not stated as a fact.

Compare:

• sabe = she knows
• sabía = she knew / used to know
• supiera = she knew, in a subjunctive sense after como si

After como si, Spanish does not normally use the indicative here.

Supiera is the imperfect subjunctive, third-person singular, of saber.

So the base verb is:

• saber = to know

And the form here is:

• supiera = she knew, in a subjunctive/irrealis sense

It is used because the sentence says as if she already knew, which presents it as an impression, not necessarily a fact.

You may also see supiese, which is another valid imperfect subjunctive form, though supiera is very common.

Here tocar means to be someone’s turn.

So:

• le toca a ella = it’s her turn

Literally, it is something like it touches to her, but you should learn it as the idiomatic expression to be someone’s turn.

Some useful examples:

• Me toca a mí = It’s my turn
• Te toca a ti = It’s your turn
• Le toca a ella = It’s her turn

It is a normal feature of Spanish called clitic doubling.

• le already means to her
• a ella is added for emphasis or clarity

So le toca a ella is not bad repetition. It is natural Spanish.

In this sentence, a ella helps underline that it is her turn, perhaps not someone else’s. It also removes ambiguity, since le could mean to him, to her, or to you in formal speech.

Ya adds the idea of already.

So:

• como si supiera = as if she knew
• como si ya supiera = as if she already knew

It gives a slight sense that she seems to know in advance that her turn has come. It makes the smile feel more anticipatory or confident.

Yes, it is the normal punctuation here.

When a subordinate clause comes first, Spanish usually separates it with a comma:

• Cuando ve el columpio libre, sonríe...

If you reversed the order, you would usually not use a comma:

• Sonríe cuando ve el columpio libre.

So the comma is standard and helps the sentence read clearly.

Yes, but the meaning would shift slightly.

• el columpio libre suggests a specific swing, probably one already relevant in the scene
• un columpio libre means a free swing, any one that happens to be available

So the original sentence feels a bit more definite and scene-based: she sees the swing free, perhaps the one she wants.