La mia coinquilina prepara sempre uno spuntino nel microonde quando torna tardi dal lavoro.

Because the noun is feminine singular: coinquilina = female roommate/flatmate.

In Italian, both the article and the possessive adjective must agree with the noun:

• la = feminine singular the
• mia = feminine singular my
• coinquilina = feminine singular noun

Compare:

• il mio coinquilino = my male roommate
• la mia coinquilina = my female roommate

Coinquilina means a female person you share an apartment/house with.

It comes from:

• co- = together/shared
• inquilina = female tenant

The masculine form is coinquilino.

Depending on context, English might translate it as:

• roommate
• flatmate
• housemate

Prepara is the third-person singular form of preparare in the present tense.

The subject is la mia coinquilina, which is she, so the verb must match she:

• io preparo = I prepare
• tu prepari = you prepare
• lui/lei prepara = he/she prepares

So:

• La mia coinquilina prepara... = My roommate prepares...

In Italian, adverbs like sempre often come after the conjugated verb:

• prepara sempre = always prepares

This is very natural word order in Italian.

You could sometimes move adverbs for emphasis, but prepara sempre is the normal, neutral pattern.

Because spuntino starts with s + consonant (sp), and masculine singular nouns with that sound usually take uno, not un.

Examples:

• uno spuntino
• uno studente
• uno zaino

But:

• un panino
• un libro

So uno spuntino is grammatically correct.

Yes, in this sentence spuntino means snack or a light bite.

It often suggests something small to eat, not a full meal.

Examples:

• fare uno spuntino = to have a snack
• uno spuntino veloce = a quick snack

So prepara sempre uno spuntino means she always makes herself something small to eat.

Nel is a contraction of in + il:

• in il → nel

So:

• nel microonde = in the microwave

Here, microonde is short for forno a microonde. In everyday Italian, people often just say il microonde.

Literally, it means in the microwave.

In practice, English might sometimes translate it more naturally as:

• in the microwave
• using the microwave

Italian often uses in with appliances in this kind of sentence:

• cuocere nel forno = cook in the oven
• scaldare nel microonde = heat in the microwave

So the phrase is perfectly natural.

Because this sentence describes a real, habitual action, so Italian uses the indicative, not the subjunctive.

• quando torna tardi dal lavoro = when she comes back late from work

Since this is about something that regularly happens, torna is the normal choice.

Torni would be subjunctive and would not fit this straightforward statement.

Both tornare and ritornare can mean to return / come back, but tornare is very common and natural in everyday Italian.

So:

• quando torna tardi dal lavoro = when she comes home late from work

Using ritorna would also be understandable, but torna sounds simpler and more idiomatic here.

Because tardi is the normal adverb meaning late.

Italian often has simple adverbs that do not end in -mente:

• presto = early / soon
• tardi = late
• bene = well
• male = badly

So:

• torna tardi = she comes back late

Tardamente exists, but it is much less common and would sound unnatural here.

Dal is the contraction of da + il:

• da il → dal

Here da means from, so:

• dal lavoro = from work

Compare:

• torna dal lavoro = comes back from work
• esce dal supermercato = exits the supermarket

Because Italian, like English, often uses the present tense for habitual actions.

This sentence means that this is her usual behavior:

• prepara sempre uno spuntino... = she always makes a snack...
• quando torna tardi dal lavoro = when she comes home late from work

So the present tense here does not mean only right now. It means generally / habitually.

Yes. The sentence follows a very typical Italian pattern:

Subject + verb + adverb + object + place + time clause

• La mia coinquilina = subject
• prepara = verb
• sempre = adverb
• uno spuntino = object
• nel microonde = place/method
• quando torna tardi dal lavoro = time clause

So the sentence sounds natural and neutral, not especially emphatic.