Se a empresa cancelar o voo de manhã, a passageira vai recusar a diária do hotel e voltar para casa.

After se meaning if, Portuguese often uses the future subjunctive when talking about a possible future situation.

So:

• Se a empresa cancelar o voo... = If the company cancels the flight...

This is the normal structure for a real future possibility.

Why not the others?

• se cancela would sound like a habitual or more general situation, like if it usually cancels
• se cancelará is not used here; Portuguese does not normally use the future indicative after se in this type of conditional clause

A useful thing to know: for many -ar verbs, the future subjunctive looks exactly like the infinitive. So cancelar here is not the plain infinitive in function, even though it looks the same.

Yes. Vai recusar is a very common way to express the future in Brazilian Portuguese.

It is the structure:

• ir + infinitive

So:

• vai recusar = will refuse / is going to refuse

You could also say:

• a passageira recusará a diária do hotel

That is the simple future, and it is grammatically correct. But in Brazil, vai + infinitive is usually more natural in everyday speech and very common in writing too.

So:

• vai recusar = more conversational and common
• recusará = more formal or literary

Because the same auxiliary verb vai applies to both infinitives:

• vai recusar
• (vai) voltar

So the sentence means:

• she is going to refuse ... and return home

Portuguese often avoids repeating the auxiliary when it is shared.

You could say:

• a passageira vai recusar a diária do hotel e vai voltar para casa

But repeating vai is not necessary, and the original version sounds smoother.

Diária is a very important hotel word in Portuguese. It usually means the charge or stay for one day/night at a hotel.

So a diária do hotel here means something like:

• the hotel night
• the hotel stay for a day
• the hotel accommodation charge

In travel-disruption contexts, it can imply that the airline/company is offering to pay for one night at a hotel. So the passenger would be refusing that hotel stay.

It does not mean diary in the English sense. Even though the words look similar, they are unrelated in meaning here.

Because de manhã is the usual expression for in the morning.

So:

• cancelar o voo de manhã = cancel the flight in the morning

By contrast, da manhã is used in different situations, such as when morning is describing a noun:

• o voo da manhã = the morning flight
• sete da manhã = seven in the morning

So the difference is:

• de manhã = during the morning
• da manhã = of the morning / morning as a label or specification

In Portuguese, casa often means home when used without an article.

So:

• voltar para casa = go back home / return home

If you add the article, para a casa, it sounds more like to the house, meaning a specific building.

Compare:

• Ela voltou para casa. = She went back home.
• Ela voltou para a casa da mãe. = She went back to her mother’s house.

So in your sentence, para casa is the natural idiomatic choice.

Portuguese uses definite articles much more often than English does.

In this sentence, the articles help mark the nouns as specific or understood from context:

• a empresa = the company
• o voo = the flight
• a passageira = the passenger
• a diária = the hotel night/daily charge
• o hotel = the hotel

English often drops the where Portuguese keeps it. For learners, this is very normal and something you gradually get used to.

Not necessarily. Empresa literally means company or business.

In this context, it probably refers to the company responsible for the trip disruption, such as:

• the airline
• a travel company
• a transport company

If the sentence wanted to be more specific, it could say:

• a companhia aérea = the airline

So empresa is broader, while companhia aérea is more precise.

Yes. You could reverse the order:

• A passageira vai recusar a diária do hotel e voltar para casa se a empresa cancelar o voo de manhã.

That means the same thing.

The original version starts with the if-clause, which is very common when setting up a condition first.

There is also a punctuation difference:

• When the se clause comes first, a comma is normally used.
• When it comes second, the comma is often omitted.

So both are correct, but the word order changes the rhythm and focus a little.

Modern Brazilian Portuguese spells it voo, with no accent.

The older spelling vôo existed before the spelling reform. Under current orthography, words like this lost the circumflex accent.

So today:

• voo = correct modern spelling
• vôo = old spelling

You may still see the old version in older books, websites, or materials.

The difference is mainly grammatical meaning.

• Se a empresa cancelar o voo de manhã...
  This refers to a possible future event: If the company cancels the flight in the morning...

• Se a empresa cancela o voo de manhã...
  This sounds more like a habitual or repeated situation: If the company cancels the flight in the morning / whenever it cancels...

For a one-time future condition, the original sentence with cancelar is the right choice.