Mi hermana tiene las pestañas muy largas y siempre le molestan cuando hace viento.

With body parts, Spanish usually prefers the definite article — el, la, los, las — when it is already obvious whose body part you mean.

So Mi hermana tiene las pestañas muy largas sounds natural because we already know the eyelashes belong to my sister.

Using sus pestañas is possible, but it would usually sound more emphatic, contrastive, or less natural in a simple description.

A similar pattern:

• Tiene el pelo largo = She has long hair
• Tiene los ojos azules = She has blue eyes

Because largas agrees with pestañas.

Pestañas is:

• feminine
• plural

So the adjective must also be:

• feminine
• plural

That gives us largas.

Quick comparison:

• la pestaña larga = the long eyelash
• las pestañas largas = the long eyelashes

In Spanish, most descriptive adjectives normally come after the noun.

So:

• pestañas largas = long eyelashes

This is the most neutral, standard order.

If an adjective comes before the noun, it often changes tone, emphasis, or style. For a basic physical description, pestañas largas is what learners should expect.

Because molestar works differently from how English learners often expect.

In this sentence, the eyelashes are the thing doing the bothering, so las pestañas is the subject.

The person affected — her — is expressed with an indirect object pronoun: le.

So the structure is basically:

• Las pestañas le molestan = Her eyelashes bother her

Not:

• La molestan = They bother her, with her as a direct object

With molestar, Spanish usually treats the person as the one affected by the annoyance, so le is the normal choice.

Because the subject of the verb is las pestañas, which is plural.

So:

• las pestañas molestan = the eyelashes bother

That is why the verb is molestan.

If the subject were singular, the verb would be singular too:

• La luz le molesta = The light bothers her
• El viento le molesta = The wind bothers her

Usually, no. This is a very important false friend.

In normal everyday Spanish, molestar usually means:

• to bother
• to annoy
• to disturb
• to cause discomfort

So here le molestan means they bother her or they annoy her.

Depending on context, English to molest is often much stronger and usually refers to sexual misconduct. In Spanish, that idea is usually expressed with other verbs, depending on the exact meaning.

So in this sentence, think bother, not molest.

Because Spanish indirect object pronouns do not show gender in the singular.

So le can mean:

• to him
• to her
• to you (formal singular)

You understand who it refers to from the context. Here, it clearly refers to mi hermana.

If needed, Spanish can make it explicit:

• A mi hermana le molestan cuando hace viento

But in your sentence, Mi hermana already gives enough context.

Because short object pronouns like me, te, le, nos, os, les normally go before a conjugated verb.

So:

• le molestan

Not:

• molestan le

This is the normal position with a finite verb.

Examples:

• Me gusta
• Te duele
• Le molestan

Cuando hace viento means when it’s windy or when there is wind.

Spanish often uses hacer in weather expressions:

• hace frío = it’s cold
• hace calor = it’s hot
• hace viento = it’s windy

So here hace viento is a standard weather expression.

You may also hear hay viento, which literally means there is wind. That is also possible in many contexts, but hace viento is very common for talking about weather conditions in a general way.

Because Spanish often omits subject pronouns when the subject is already clear.

Here, Mi hermana has already been mentioned, so there is no need to say ella again.

Spanish prefers:

• Mi hermana tiene las pestañas muy largas y siempre le molestan...

Rather than:

• Mi hermana tiene las pestañas muy largas y ella siempre...

Adding ella is possible, but it would usually add emphasis or contrast.

That is a very natural place for an adverb like siempre.

In Spanish, adverbs of frequency such as siempre, nunca, and a menudo often go:

• before the verb phrase, or
• in another nearby position, depending on emphasis

So siempre le molestan means they always bother her.

This word order sounds completely normal and natural.