Mi hermana sabe preparar una tortilla de patata.

In modern standard Spanish, possessive words like mi, tu, su, nuestro usually go directly before the noun without an article:

• mi hermana = my sister
• tu casa = your house

Using an article as well, like la mi hermana, is not normal in standard Spanish.

Spanish often leaves out subject pronouns because the verb ending already shows who the subject is.

• sabe = he/she/it knows or he/she can

So Mi hermana sabe... already clearly means My sister knows... / My sister can..., and adding ella would usually be unnecessary unless you want emphasis or contrast.

Here, saber + infinitive means to know how to do something.

So:

• sabe preparar = knows how to make / can prepare

This is different from saber meaning to know a fact:

• Sé la respuesta. = I know the answer.
• Sé cocinar. = I know how to cook.

In this sentence, it is the know how to meaning.

Because after saber when you mean know how to do something, Spanish uses an infinitive:

• sabe cocinar = knows how to cook
• sabe conducir = knows how to drive
• sabe preparar = knows how to prepare

This is similar to English knows how to prepare, where prepare stays in the base form.

Spanish has two common verbs that can translate as to know:

• saber = to know information, or to know how to do something
• conocer = to be familiar with a person, place, or thing

So you say:

• Mi hermana sabe preparar una tortilla de patata.
• Mi hermana conoce Madrid.

You would not use conoce preparar here, because the sentence is about a skill.

Una is the feminine singular indefinite article, meaning a or an.

• una tortilla de patata = a potato omelette / a Spanish omelette

It is used because tortilla is a singular countable noun and it is feminine.

Because it takes feminine words with it:

• una tortilla
• la tortilla

In Spanish, many nouns ending in -a are feminine, and tortilla is one of them. That is why the article is una, not un.

In Spanish, ingredient descriptions often use de + singular noun, even when English might think of the ingredient more generally.

So tortilla de patata is the standard name in Spain for the dish. You may also hear tortilla de patatas, and both are used, but tortilla de patata is very common.

This is really a set expression for the dish, not something you should analyze too literally word by word.

Not in this sentence. In Spain, tortilla usually means an omelette, especially tortilla de patata, a famous Spanish dish made with egg and potato.

So in Spain:

• tortilla de patata = Spanish omelette

This is different from the thin flatbread called tortilla in Mexican Spanish and in English.

Yes, but the meaning changes slightly because the subject becomes less explicit.

• Mi hermana sabe preparar una tortilla de patata. = My sister knows how to make a Spanish omelette.
• Sabe preparar una tortilla de patata. = He/She knows how to make a Spanish omelette.

Without mi hermana, Spanish relies on context to know who he/she is.

Yes, but it means something slightly different.

• sabe preparar = knows how to make it, has the skill
• puede preparar = can make it, is able to make it, possibly because circumstances allow it

So:

• Mi hermana sabe preparar una tortilla de patata. = She has learned how to do it.
• Mi hermana puede preparar una tortilla de patata. = She is able to do it, perhaps now or in this situation.

In this sentence, sabe preparar is the more natural choice for talking about cooking skill.

Spanish word order is more flexible than English, but the normal and most natural order here is:

• Mi hermana sabe preparar una tortilla de patata.

A version like Una tortilla de patata sabe preparar mi hermana is grammatically possible in a special context, but it sounds marked and would usually be used for emphasis or contrast, not as a neutral sentence.

So for everyday Spanish, stick with the original order.

Saber is an irregular verb. In the present tense:

• yo sé
• tú sabes
• él/ella/usted sabe
• nosotros sabemos
• vosotros sabéis
• ellos/ellas/ustedes saben

So sabe is the third person singular form, matching mi hermana.

The sentence is already natural in Spain Spanish. Another very common way to say it would be:

• Mi hermana sabe hacer tortilla de patata.

Both preparar and hacer work, but hacer is often especially common in everyday speech for food:

• hacer una tortilla
• hacer paella
• hacer la cena

So the original sentence is correct, but hacer may sound a bit more conversational.