A tosse dela costuma piorar à noite, então ela fica quieta.

Her cough usually gets worse at night, so she stays quiet.

Breakdown of A tosse dela costuma piorar à noite, então ela fica quieta.

• dela: her
• então: so
• ela: she
• quieto: quiet
• à noite: at night
• a tosse: the cough
• costumar: to tend to / to usually (do)
• piorar: to get worse
• ficar: to stay / to become

Questions & Answers about A tosse dela costuma piorar à noite, então ela fica quieta.

Why is it A tosse dela and not A tosse de ela?

In Portuguese, the preposition de + a personal pronoun changes form. De + ela becomes dela (meaning of hers / her).
Other common ones: dele (de + ele), deles (de + eles), delas (de + elas).
So A tosse dela = Her cough.

Does dela mean her or hers here?

In this structure ([noun] + dela), it functions like English her: her cough.
But grammatically it’s closer to “of hers,” and it can also stand alone like hers in some contexts (e.g., A culpa é dela = It’s her fault / “The blame is hers”).

What does costuma mean here, and why not just use present tense like piora?

Costuma comes from costumar = to usually / tend to.
So costuma piorar means usually gets worse / tends to get worse—it emphasizes a repeated habit/pattern.
If you said A tosse dela piora à noite, that’s also possible and means Her cough gets worse at night, but it can sound a bit more direct/absolute. Costuma softens it to “as a general rule.”

Why is the next verb in the infinitive: costuma piorar?

After costumar, Portuguese normally uses an infinitive: costumar + infinitive.
Examples: Eu costumo acordar cedo (I usually wake up early), Ele costuma chegar tarde (He tends to arrive late).

What’s the difference between piorar and ficar pior?

Both can mean to get worse, but:

• piorar is a single verb meaning to worsen / get worse.
• ficar pior uses ficar (to become) + adjective: to become worse.

In many everyday contexts they’re interchangeable:
A tosse piora ≈ A tosse fica pior.

Why is it à noite with the accent (crase)?

À = a + a (preposition a + feminine article a).
The expression à noite literally means “at the night,” which Portuguese treats as feminine and uses the article: a noite.
So you write à noite (crase). Similar: à tarde (in the afternoon), à manhã (in the morning; less common than de manhã).

Could it also be de noite instead of à noite?

Yes. In Brazilian Portuguese, both exist, but they can feel slightly different:

• à noite = at night (time period when something happens; very common in formal/neutral speech)
• de noite = also at night, often more casual and sometimes more like during the night / nighttime
  In many sentences they’re interchangeable.

What does então mean here—then or so?

Here então means so / therefore, showing a consequence:
..., então ela fica quieta. = ..., so she stays quiet.
It can also mean then in sequences (Aí ele chegou, então eu saí), but with a cause→result structure it often reads as so.

Why is it ela fica quieta and not ela é quieta?

Ficar + adjective often means to become / to stay in a certain state.
So ela fica quieta means she stays quiet (or becomes quiet) in that situation.
Ela é quieta describes a more general characteristic: She is a quiet person.

Does ficar quieta mean she becomes quiet, or that she stays quiet?

It can mean either depending on context:

• becomes quiet (she quiets down)
• stays quiet (she remains quiet)

In this sentence, because it’s a reaction to her cough worsening at night, it often implies she stays/keeps quiet to avoid coughing more, discomfort, etc.

Why is quieta feminine?

Adjectives agree with the subject. The subject is ela (she), so the adjective is feminine: quieta.
If it were ele, you’d say ele fica quieto.

Could I replace quieta with em silêncio?

Often, yes, but the nuance changes:

• ficar quieta can mean stay quiet (not speaking, not making noise, maybe also “keep still” depending on context).
• ficar em silêncio is more specifically remain in silence (not speaking).

So ela fica em silêncio is a bit more explicit about silence, while quieta is broader.

Is the comma before então necessary?

It’s very common and recommended, because então is introducing a result clause. The comma helps readability:
A tosse dela costuma piorar à noite, então ela fica quieta.
In informal writing, people sometimes omit it, but the comma is a good default.

Can this be said in a more natural “spoken” way?

Yes, a couple of common spoken alternatives in Brazilian Portuguese:

• A tosse dela piora de noite, então ela fica quieta.
• À noite a tosse dela costuma piorar, então ela fica quieta.
  All are natural; choice depends on emphasis and style.

Could I say tende a piorar instead of costuma piorar?

Yes. Tende a piorar = tends to get worse and is very similar in meaning.
Nuance:

• costuma piorar stresses habitual frequency (usually happens)
• tende a piorar can feel a bit more general/clinical (a tendency), and it requires a: tender a + infinitive.

Why do we repeat ela in the second clause instead of dropping it?

Portuguese can drop subject pronouns, but in Brazilian Portuguese they’re often kept for clarity and naturalness.
You could say: ..., então fica quieta.
But many speakers prefer ..., então ela fica quieta to make the subject explicit, especially in writing or if there could be ambiguity about who becomes quiet.