Fa dos dies que la meva germana té febre.

Yes. Fer usually means to do or to make, and fa is the 3rd person singular form.

But in time expressions, Catalan uses fa impersonally, with the meaning of ago or for ... now, depending on the context.

So in:

Fa dos dies que la meva germana té febre

fa dos dies que means something like it has been two days that...

A very natural English equivalent is:

My sister has had a fever for two days.

So here fa is not really about doing anything. It is part of a fixed time expression.

Because Catalan often uses:

fa + period of time + que + present tense

to express an action or state that started in the past and is still continuing now.

So:

• Fa dos dies que la meva germana té febre
  = My sister has had a fever for two days

Even though English often uses the present perfect, Catalan commonly uses the present here.

This is one of the most important things for English speakers to notice:

• English: has had
• Catalan: té

In this structure, que links the time expression to the clause that follows.

So the pattern is:

fa + time expression + que + clause

Example:

• Fa dos dies que plou = It has been raining for two days
• Fa un any que visc aquí = I have lived here for a year

You do not usually translate que word for word here. It is just part of the normal Catalan pattern.

Catalan normally uses the definite article together with a possessive before family nouns and many other nouns:

• la meva germana = my sister
• el meu pare = my father
• la nostra casa = our house

This is more natural in standard Catalan than leaving out the article.

So for an English speaker, it may feel like Catalan is saying the my sister, but that is just how the language works.

Yes. That is also correct.

• Fa dos dies que la meva germana té febre
• La meva germana té febre des de fa dos dies

Both mean essentially the same thing: My sister has had a fever for two days.

The difference is mostly one of structure and emphasis:

• Fa dos dies que... starts with the duration
• ...des de fa dos dies puts the main statement first and adds the duration afterward

Both are common and natural.

No. Fa dos dies is the normal expression.

Catalan does not usually move it around the way English sometimes can with time phrases. In this pattern, the standard order is:

Fa + time + que + clause

So:

• Fa dos dies que la meva germana té febre ✔
• Dos dies fa que la meva germana té febre ✘ or very unnatural in normal usage

Stick with fa dos dies que.

Not exactly. This is a very important distinction.

On its own, fa dos dies can mean two days ago:

• Va arribar fa dos dies = He arrived two days ago

But in this sentence, because it is followed by que + present tense, it means:

for two days now / it has been two days that...

So compare:

• Va arribar fa dos dies = a completed event two days ago
• Fa dos dies que té febre = a state that began two days ago and continues now

In Catalan, as in English, some health conditions are often expressed without an indefinite article.

So:

• té febre = has a fever
• té son = is sleepy
• té gana = is hungry
• té por = is afraid

Even though English says a fever, Catalan normally just says febre after tenir.

So té febre is the standard expression.

Yes. Catalan is a pro-drop language, so subject pronouns are often omitted when the verb already makes the subject clear.

But in this sentence, the subject is not a pronoun like she. It is the noun phrase la meva germana, and it is included because we need to say who has the fever.

If the person were already clear from context, Catalan might say:

• Fa dos dies que té febre

That would mean:

• She has had a fever for two days
• or He has had a fever for two days

depending on context.

So Catalan can omit the subject pronoun, but not the subject information when it is needed.

The accent in té helps distinguish it from te.

• té = he/she has or has
• te = you in some dialectal or informal uses, or part of other forms

In standard written Catalan, the accent marks the stressed vowel and also helps avoid confusion.

So:

• la meva germana té febre = my sister has a fever

The accent is important in writing.

It describes a situation that is understood to be still true now.

Because the structure is:

fa + time + que + present

it normally means the action or state started in the past and continues into the present.

So this sentence implies that your sister still has a fever now.

If the fever were already over, Catalan would normally use a different structure, for example with a past tense, depending on exactly what you want to say.