La niña pestañeó varias veces porque tenía arena en los ojos.

Pestañeó is the preterite form of pestañear, meaning to blink.

• pestañear = to blink
• pestañeó = she blinked

It is third-person singular preterite, so it matches la niña.

This is a very common Spanish past-tense contrast:

• pestañeó = preterite, for a completed action
• tenía = imperfect, for a background condition or ongoing state

So the sentence presents:

• the blinking as the main event: she blinked several times
• the sand in her eyes as the reason/background situation: because she had sand in her eyes

In other words:

• pestañeó = what happened
• tenía = what was going on

Varias veces means several times.

Vez means time in the sense of an occurrence, as in:

• una vez = once / one time
• dos veces = twice / two times
• varias veces = several times

It is plural because varias refers to more than one occurrence.

La niña means the girl, while una niña means a girl.

Using la suggests that the girl is already known in the context, or that the speaker is referring to a specific girl. Spanish often uses the definite article where English might also use the.

Both are grammatically possible, but they give a different feel:

• La niña pestañeó... = the girl blinked...
• Una niña pestañeó... = a girl blinked...

Arena is normally an uncountable noun in Spanish, just like sand in English.

So Spanish says:

• tenía arena en los ojos = she had sand in her eyes

Not usually:

• arenas for ordinary sand in this context

The plural arenas can exist, but it usually means types of sand, sandy areas, or is used in more specialized contexts.

Spanish often uses the definite article with body parts when the owner is already clear.

So:

• tenía arena en los ojos = literally she had sand in the eyes
• but naturally understood as in her eyes

This is very normal in Spanish. Using sus ojos is possible, but it often sounds more emphatic, contrastive, or less natural in a simple sentence like this.

Compare:

• Me duele la cabeza = My head hurts
• Se lavó las manos = He/She washed his/her hands

Same pattern.

Here porque means because, so it is written as one word, no accent.

This is one of the classic Spanish spelling distinctions:

• porque = because
• por qué = why
• el porqué = the reason / the why
• por que = less common combination, used in specific structures

In this sentence, it introduces the reason, so porque is correct.

Both can mean to blink.

In many contexts, they are very similar, and either one may be understood. However:

• parpadear is often the more general and common verb for blinking
• pestañear also means to blink, but is connected more directly to pestañas (eyelashes)

For a learner, it is enough to know that pestañó / parpadeó can both refer to blinking, though native usage may vary by region and context.

The letter ñ is a separate letter in Spanish. It is not just n with an accent.

It sounds roughly like:

• ny in canyon
• or the gn in some pronunciations of lasagna

So:

• niña sounds roughly like NEEN-ya
• pestañeó includes that same ny sound

This is an important sound distinction:

• ano and año are different words
• n and ñ are different letters

The accent mark in pestañeó shows the correct stress.

Without getting too deep into spelling rules, the accent helps show that the ending is pronounced in a way that keeps the stress where it belongs:

• pes-ta-ñe-Ó

This is the preterite ending for many -ar verbs in the él/ella/usted form:

• habló
• miró
• lloró
• pestañeó

The accent is written because it is part of the standard spelling of that form.

Tenía has an accent because it is part of the imperfect form of tener:

• yo tenía
• tú tenías
• él/ella tenía
• nosotros teníamos

The accent marks the correct stress and helps distinguish pronunciation. You should learn tenía as the normal written form of he/she had in the imperfect.

You could say it, but it would mean something slightly different.

• tenía arena en los ojos = she had sand in her eyes
• había arena en los ojos = there was sand in her eyes

The original sentence focuses on the girl and her condition, so tenía is the natural choice.

Yes. Spanish word order is flexible, though some versions are more natural depending on context.

Original:

• La niña pestañeó varias veces porque tenía arena en los ojos.

You could also say:

• Porque tenía arena en los ojos, la niña pestañeó varias veces.

This puts more emphasis on the reason first. Both are correct.

Because the sentence refers to both eyes.

If it were only one eye, you would say:

• tenía arena en el ojo = she had sand in her eye

Since irritation from sand often affects both eyes, the plural is natural here.