Learn Hardcore Spanish (Latin America): Ella tiene fiebre y muestra el primer síntoma: dolor de cabeza. - She has a fever and shows the first symptom: a headache.

You can drop it. Spanish is a pro‑drop language, so Tiene fiebre y muestra el primer síntoma: dolor de cabeza is perfectly natural. Keep ella only for emphasis, contrast, or clarity (e.g., Ella tiene fiebre, pero él no).

Why is it tiene fiebre and not está fiebre?

Spanish typically uses tener + noun for physical states: tener fiebre, tener hambre, tener sed, tener sueño. You can also hear estar con fiebre in much of Latin America, and le dio fiebre to mean “she came down with a fever.” Avoid está fiebre or es fiebre—those are ungrammatical.

Is fiebre countable? Should I say una fiebre?

Usually it’s uncountable: tiene fiebre (no article). You may use an article when specifying type/degree:

tiene fiebre alta (more common) / tiene una fiebre muy alta (also heard)
tuvo una fiebre tifoidea Colloquial: tiene 39 de fiebre (she has a 39°C fever).

Is muestra the best verb here, or would presenta sound more natural?

Both work. Muestra = “shows/displays” (neutral). Presenta is very common in medical or formal contexts. Everyday alternatives: tiene como primer síntoma…, manifiesta…, empieza con….

Why primer and not primero?

It’s the apocopated form. Primero drops the final -o before a masculine singular noun: el primer síntoma, el primer día. When it stands alone, keep primero: Es el primero.

Is síntoma masculine or feminine?

Masculine: el síntoma / los síntomas. Like other Greek-origin words ending in -ma: el problema, el tema, el sistema, el clima.

Why is there a colon before dolor de cabeza? Could I write it another way?

The colon introduces an explanation/apposition (the specific symptom). Alternatives:

…y el primer síntoma es (el) dolor de cabeza.
…y muestra como primer síntoma el dolor de cabeza. In Spanish, the word after a colon is not capitalized unless it’s a proper name or quoted speech.

Should it be un dolor de cabeza, el dolor de cabeza, or no article?

All are possible, with different nuances:

Label/generic: primer síntoma: dolor de cabeza (no article, like a list).
Specific instance: El primer síntoma es un dolor de cabeza fuerte.
Talking about the category: El primer síntoma es el dolor de cabeza.

What’s another common way to say someone has a headache?

Le duele la cabeza (“her head hurts”). Pattern:

Me duele la cabeza.
Te duele la cabeza.
Le duele la cabeza. It’s equivalent in meaning to tiene dolor de cabeza, but it highlights the experience of pain.

Does y ever change to e? Should it here?

It changes to e before words that begin with the vowel sound /i/ (spelled i- or hi-): fiebre e hipotermia, padres e hijos. It does not change before words starting with hie- (pronounced like ye-), so you’d say agua y hielo. In your sentence, no change is needed: …fiebre y muestra….

How do I pronounce tricky parts in Latin American Spanish?

cabeza: the z sounds like s (seseo): ca-BE-sa.
síntoma: stress on the first syllable: SÍN-to-ma (the accent mark shows this).
fiebre: the ie is a diphthong: FYE-bre.
muestra: ue diphthong: MWES-tra; single r is a tap.
y (the conjunction) sounds like a short “ee.”

Could I use the present progressive: está mostrando?

You can, but Spanish usually prefers the simple present for current states: muestra. Use está mostrando only to emphasize an ongoing, temporary process: Está mostrando mejoría hoy.

Can I simplify it to Tiene fiebre y dolor de cabeza?

Yes. That’s a very natural everyday way to say it, without the explanatory colon or muestra.

Are there regional synonyms for dolor de cabeza?

Yes:

migraña: migraine (specific diagnosis).
jaqueca: often used for migraine in many countries.
cefalea: formal/medical term. For a generic headache, dolor de cabeza is the safest choice everywhere.

Why not la primer síntoma?

Because síntoma is masculine. The correct phrase is el primer síntoma. If the noun were feminine, you’d say la primera señal, la primera pista, etc.

Is the accent on síntoma required?

Yes. It’s síntoma (accent on the first syllable). Without the accent (sintoma) it’s misspelled and may mislead stress.