Minha irmã deixou a bolsa no sofá e esqueceu o batom no banheiro.

Because minha has to agree with the noun it describes, and irmã is a feminine singular noun.

• meu = my, for a masculine singular noun
• minha = my, for a feminine singular noun

Compare:

• meu irmão = my brother
• minha irmã = my sister

So the possessive agrees with irmã, not with the speaker.

In Brazilian Portuguese, using an article before a possessive is often optional, especially in everyday speech.

So both of these are possible:

• Minha irmã deixou a bolsa...
• A minha irmã deixou a bolsa...

In Brazil, the version without the article is very common. In some regions or styles, people use the article more often.

They are in the preterite (simple past), third person singular.

That means they describe completed actions in the past:

• deixou = left
• esqueceu = forgot

The subject is minha irmã, so the verb is in he/she/it form:

• eu deixei
• você/ela deixou

and

• eu esqueci
• você/ela esqueceu

Because Portuguese often leaves out the subject when it is already clear from context.

So:

• Minha irmã deixou a bolsa no sofá e esqueceu o batom no banheiro.

naturally means:

• My sister left the purse on the sofa and (she) forgot the lipstick in the bathroom.

Repeating minha irmã would sound unnecessary here.

They express two different ideas:

• deixar here means to leave something somewhere
• esquecer means to forget

So:

• deixou a bolsa no sofá = she left the purse on the sofa
• esqueceu o batom no banheiro = she forgot the lipstick in the bathroom

A useful point: deixar does not automatically mean the action was accidental. It just says the bag was left there. But esquecer clearly shows forgetfulness.

Because nouns in Portuguese have grammatical gender.

• bolsa is feminine, so it takes a
• batom is masculine, so it takes o

So:

• a bolsa
• o batom

This grammatical gender does not necessarily have anything to do with biological sex. Objects are simply classified as masculine or feminine.

Because no is a contraction of:

• em + o = no

Since both sofá and banheiro are masculine nouns, you get:

• no sofá
• no banheiro

If the noun were feminine, you would use:

• em + a = na

For example:

• na mesa
• na cozinha

This is a very common question. Portuguese often uses em (and contractions like no/na) in places where English uses different prepositions such as in, on, or at.

So:

• no sofá = on the sofa
• no banheiro = in the bathroom

You should not translate em word-for-word every time. Its exact English equivalent depends on context.

Yes. While many nouns ending in -a are feminine, sofá ends in a stressed -á and is masculine:

• o sofá

This is a good reminder that noun endings are helpful clues, but not perfect rules. Gender often has to be learned with the noun:

• o sofá
• a bolsa
• o banheiro
• o batom

Because the word batom is grammatically masculine in Portuguese:

• o batom

There is no strong meaning-based reason that helps here; it is just the gender the noun has in Portuguese. This is very normal. Many object nouns simply have to be memorized together with their article.

A good habit is to learn nouns as a unit:

• o batom
• a bolsa
• o sofá

not just batom, bolsa, sofá by themselves.

Yes. Grammatically, you can switch the locations if that is what you want to say.

The structure is:

• [subject] + [verb] + [object] + [place]

So these are both grammatical:

• Minha irmã deixou a bolsa no sofá e esqueceu o batom no banheiro.
• Minha irmã deixou a bolsa no banheiro e esqueceu o batom no sofá.

Only the meaning changes.

Yes. Deixar is a very common verb with more than one meaning.

It can mean:

• to leave
• to let / allow

Examples:

• Ela deixou a bolsa no sofá. = She left the purse on the sofa.
• Ela deixou o irmão sair. = She let her brother go out.

In your sentence, the meaning is clearly to leave something somewhere.

A natural version could be:

• Minha irmã a deixou no sofá e o esqueceu no banheiro.

But this sounds less natural in everyday Brazilian Portuguese than repeating the nouns, especially in a simple sentence like this.

In spoken Brazilian Portuguese, people often prefer the full nouns or different structures rather than object pronouns in many casual contexts.

So the original sentence is very natural:

• Minha irmã deixou a bolsa no sofá e esqueceu o batom no banheiro.