Minha tia disse que vai sozinha à reunião na quarta-feira.

Because minha has to agree with tia, the thing being possessed.

• tia is feminine singular
• so the possessive must also be feminine singular: minha

Examples:

• meu tio = my uncle
• minha tia = my aunt
• meus tios = my uncles / my aunt and uncle
• minhas tias = my aunts

In Portuguese, possessives agree with the noun that follows, not with the speaker.

Portuguese often leaves out subject pronouns when the subject is clear from context.

Here, after Minha tia disse que..., the understood subject of vai is still minha tia. So ela is not necessary.

• Natural: Minha tia disse que vai sozinha à reunião
• Also possible: Minha tia disse que ela vai sozinha à reunião

Adding ela can sound more explicit, and sometimes more emphatic, but it is often omitted in normal speech and writing.

Disse que introduces reported speech or an indirect statement.

• disse = said
• que = that

So the structure is basically:

• Minha tia disse que...
• My aunt said that...

This is very common in Portuguese after verbs like:

• dizer = to say
• achar = to think
• saber = to know
• ver = to see

Examples:

• Ele disse que chega cedo.
• Achei que você estava em casa.

Usually, no.

In English, you can often say:

• My aunt said she is going...

In Portuguese, que is normally kept:

• Minha tia disse que vai...

Leaving it out is generally not standard and will sound wrong to many learners and speakers in this kind of sentence.

So for learners, the safe rule is:

• after disse, use que

All of those are possible depending on context.

Vai is the 3rd person singular present of ir = to go.

So literally, it is present tense:

• ela vai = she goes / she is going

But in Portuguese, the present tense is often used for a planned or expected future action, especially when there is a time expression.

Here, na quarta-feira makes it sound future-oriented:

• she is going on Wednesday
• she will go on Wednesday

So this is a normal, natural use of the present tense for the near or scheduled future.

Because it refers to minha tia, which is feminine.

The base form is:

• sozinho = alone, by oneself masculine
• sozinha = alone, by oneself feminine

Here it describes how your aunt is going, so it agrees with her:

• Meu tio vai sozinho.
• Minha tia vai sozinha.

Even though English uses alone as an adverb-like word, Portuguese often uses sozinho/sozinha in a form that still agrees with the person it refers to.

It behaves like an adjective that agrees with the subject, even though in English we might translate it with something adverb-like, such as alone.

In:

• vai sozinha

sozinha describes the subject: she goes alone.

That is why it changes form:

• sozinho
• sozinha
• sozinhos
• sozinhas

So even if the English translation feels adverbial, Portuguese still shows agreement.

Because this is a + a = à.

This is called crase.

What is happening:

• the verb ir can take the preposition a
• reunião here uses the feminine article a

So:

• a + a reunião → à reunião

Examples:

• Vou à escola.
• Ela foi à praia.

Compare:

• Vou ao mercado. = a + o
• Vou à reunião. = a + a

The accent in à is not just a stress mark; it shows this contraction.

Because na is the contraction of em + a.

• em = in / on
• a quarta-feira = Wednesday

So:

• em a quarta-feira → na quarta-feira

In English, this is usually on Wednesday.

This is very common with days and dates in Portuguese when a preposition is used.

Examples:

• na segunda-feira
• na terça-feira
• na quarta-feira

In this sentence, it most naturally means a specific Wednesday, probably the upcoming one or one already known in context.

If you want to say every Wednesday, Portuguese more often uses:

• às quartas-feiras
• toda quarta-feira

Examples:

• Ela vai à reunião toda quarta-feira. = She goes to the meeting every Wednesday.
• Ela vai à reunião às quartas-feiras. = She goes to the meeting on Wednesdays.

So in your sentence, the singular form strongly suggests one particular Wednesday.

In Portuguese, days of the week are normally not capitalized, unless they begin a sentence.

So:

• segunda-feira
• terça-feira
• quarta-feira

And yes, quarta-feira is normally written with a hyphen.

This is different from English, where Wednesday is capitalized.

Yes. Portuguese allows some flexibility, although the original sentence is very natural.

Possible alternatives:

• Minha tia disse que vai à reunião sozinha na quarta-feira.
• Minha tia disse que, na quarta-feira, vai sozinha à reunião.

The original:

• Minha tia disse que vai sozinha à reunião na quarta-feira.

This version puts sozinha close to vai, which makes the idea of going alone stand out clearly.

Changing the order can slightly shift emphasis, but the basic meaning stays the same.

Yes.

In Portuguese, ir a uma reunião can mean literally go to the meeting, but in many contexts it also implies be present at / attend the meeting.

So the sentence may focus less on the physical movement and more on the fact that she will be there, and that she will be there alone.

That is very normal usage.

Reunião is pronounced roughly like reh-oo-nee-OWN, but with a nasal ending.

The final -ão is one of the most important Portuguese sounds. It is not exactly like English own. The vowel is nasalized.

A rough breakdown:

• reu
• ni
• ão

Stress falls on the last syllable:

• reu-ni-ÃO

You do not need a perfect English equivalent; the key point is that -ão is nasal and stressed.

Yes, it sounds natural.

It has several very normal features of Brazilian Portuguese:

• omitted subject pronoun
• disse que for reported speech
• present tense with future meaning
• agreement in sozinha
• contraction in à reunião
• na quarta-feira for on Wednesday

A Brazilian speaker would understand it immediately and find it natural.