Mi hermana quiere cortarse el flequillo antes de la entrevista.

Because after querer (to want), Spanish normally uses an infinitive.

• quiere cortar = wants to cut
• quiere cortarse = wants to cut her own ...

So the structure is:

• [subject] + querer + infinitive

Examples:

• Quiero comer. = I want to eat.
• Ella quiere dormir. = She wants to sleep.
• Mi hermana quiere cortarse el flequillo. = My sister wants to cut her bangs.

Spanish does not say quiere se corta here.

The se shows that the action is being done to herself. In this sentence, your sister wants to cut her own bangs, not someone else’s.

• cortar = to cut
• cortarse = to cut one’s own hair / cut something on oneself

This is a very common pattern with personal grooming actions in Spanish.

Compare:

• Mi hermana quiere cortar el flequillo.
  This sounds like she wants to cut the bangs, but it does not clearly show whose. It could even sound more general.
• Mi hermana quiere cortarse el flequillo.
  Clearly means she wants to cut her own bangs.

Yes. With a conjugated verb + infinitive structure, the reflexive pronoun can usually go in two places:

1. Attached to the infinitive:

   • Mi hermana quiere cortarse el flequillo.

2. Before the conjugated verb:

   • Mi hermana se quiere cortar el flequillo.

Both are correct and mean the same thing.

Spanish often allows this with infinitives:

• Voy a ducharme.
• Me voy a duchar.

Spanish very often uses the definite article (el, la, los, las) instead of a possessive adjective (mi, tu, su) when talking about body parts, clothing, and personal items, especially when it is already clear who they belong to.

So:

• cortarse el flequillo literally looks like cut herself the bangs
• but it naturally means cut her bangs

This is very common:

• Me lavo las manos. = I wash my hands.
• Se cepilla los dientes. = He/She brushes his/her teeth.

Using su flequillo is not impossible, but el flequillo sounds more natural here.

In Spain, flequillo is the normal word for the hair at the front that falls over the forehead.

For a British English speaker, it usually corresponds to fringe.
For an American English speaker, it usually corresponds to bangs.

So:

• Spain: flequillo
• UK English: fringe
• US English: bangs

This is a good example of how the Spanish (Spain) word may line up better with British vocabulary than with American vocabulary.

Because antes is followed by de when it introduces a noun.

• antes de la entrevista = before the interview
• antes de comer = before eating

So the pattern is:

• antes de + noun
• antes de + infinitive

Examples:

• antes de clase = before class
• antes de salir = before going out

Without de, it would be incorrect here.

Spanish often uses the definite article more frequently than English does.

Here, la entrevista refers to a specific interview that both speaker and listener can identify from context.

So:

• antes de la entrevista = before the interview

If you said antes de entrevista, that would be ungrammatical in standard Spanish.

Not normally. Cortarse el flequillo most naturally means she wants to cut her own bangs.

If you want to say she wants someone else to cut them, Spanish would usually express that differently, for example:

• Mi hermana quiere que le corten el flequillo antes de la entrevista.
  = My sister wants them to cut her bangs before the interview.

Or:

• Mi hermana quiere ir a cortarse el flequillo...
  This often suggests going somewhere like a hairdresser’s, depending on context.

So the original sentence most strongly suggests she herself is going to do it.

Quiere is the third person singular present tense of querer.

Full present tense of querer:

• yo quiero
• tú quieres
• él / ella / usted quiere
• nosotros queremos
• vosotros queréis
• ellos / ellas / ustedes quieren

In your sentence:

• Mi hermana = she
• so the verb is quiere

Because querer is a stem-changing verb in the present tense:

• e → ie

So:

• querer
• quiero
• quieres
• quiere
• queremos
• queréis
• quieren

Notice that nosotros and vosotros do not change the stem:

• queremos
• queréis

This kind of change is very common in Spanish:

• pensar → pienso
• cerrar → cierra
• empezar → empieza

Yes, Mi hermana means my sister, but Spanish often does not need an explicit subject if the verb ending already makes it clear.

For example:

• Quiere cortarse el flequillo antes de la entrevista.

This could still mean:

• She wants to cut her bangs before the interview

However, in your sentence, Mi hermana is included because the speaker wants to make clear who is being talked about.

Spanish often includes the subject:

• for clarity
• for emphasis
• when introducing a new person into the conversation

Yes, but the original order is the most neutral and natural.

Standard order:

• Mi hermana quiere cortarse el flequillo antes de la entrevista.

You might also hear variations for emphasis, such as:

• Antes de la entrevista, mi hermana quiere cortarse el flequillo.

That puts more focus on the time phrase before the interview.

But for a learner, the original order is the best model:

• Subject + verb + infinitive phrase + time phrase

Yes: flequillo is especially useful for Spain Spanish.

Learners often notice more regional differences in vocabulary than in grammar. The grammar here is standard Spanish, but the vocabulary item flequillo is one of those words you definitely want for Spain.

So if you are learning Spanish from Spain, this sentence sounds very natural:

• Mi hermana quiere cortarse el flequillo antes de la entrevista.

The main Spain-specific point is the word flequillo, not the structure.