نريد زيارة صديقتي في المساء لأنها مريضة.

Because in Arabic, the verb itself often tells you who is doing the action.

• نريد means we want
• The نـ at the beginning shows we

So Arabic usually does not need a separate pronoun like نحن (we) unless you want extra emphasis.

• نريد زيارة صديقتي = We want to visit my friend
• نحن نريد زيارة صديقتي = We want to visit my friend (with extra emphasis on we)

زيارة is a verbal noun (also called a masdar) meaning visiting or visit.

Arabic often uses this pattern after verbs like want:

• نريد زيارة صديقتي literally: We want visiting my friend
• Natural English: We want to visit my friend

This is very common in Arabic. You could also say:

• نريد أن نزور صديقتي

That also means We want to visit my friend. Both are correct.

صديقتي means my friend when referring to a female friend.

Breakdown:

• صديقة = a female friend
• ـي = my

So:

• صديقتي = my female friend

The ending ـي is a attached possessive pronoun.

Because the friend is female.

• صديق = male friend
• صديقة = female friend

In this sentence, the later word مريضة also shows that the person is feminine, so everything matches a female referent.

The letter ة (taa marbuuTa) behaves differently depending on what comes after it.

When the word stands alone, it is often pronounced like -a:

• صديقة ≈ ṣadīqa

But when a suffix is attached, the t sound appears:

• صديقتي = ṣadīqatī

So the ة becomes clearly t before ـي.

في المساء means in the evening.

Breakdown:

• في = in
• المساء = the evening

The الـ means the, so this is literally in the evening.

Arabic often uses the definite article in time expressions like this:

• في الصباح = in the morning
• في المساء = in the evening
• في الليل = at night / in the night

Because it is made of:

• لأن = because
• ها = she / her

Together:

• لأنها = because she

In Arabic, object and pronoun elements are often attached directly to words rather than written separately.

In standard Arabic, after لأنّ, a pronoun is normally attached directly.

So you say:

• لأنها = because she
• لأنه = because he
• لأنهم = because they

Using لأن هي would not be the normal MSA structure here.

Because it describes the female friend.

• مريض = sick (masculine)
• مريضة = sick (feminine)

Since صديقتي refers to a woman, the adjective must agree with it in gender:

• صديقتي مريضة = My friend is sick

In Arabic, the present tense usually does not use a separate word for is / am / are.

So:

• هي مريضة literally: she sick
• Natural English: she is sick

This is normal in Arabic nominal sentences.

If you wanted the past, then Arabic would use a verb:

• كانت مريضة = she was sick

Because Arabic expresses this idea differently.

English says:

• want to visit

Arabic can say:

• نريد زيارة... using a verbal noun (visit/visiting) or
• نريد أن نزور... using أن
  • a verb

So Arabic does not need a direct equivalent of English to in the same way.

Yes. That is completely correct.

Compare:

• نريد زيارة صديقتي...
• نريد أن نزور صديقتي...

Both mean We want to visit my friend...

The first uses a verbal noun (زيارة). The second uses أن + verb (أن نزور).

Both are natural in MSA.

Because Arabic often links a verbal noun directly to what it affects.

So:

• زيارة صديقتي = visiting my friend / the visit of my friend depending on context

Here it means visiting my friend.

This is a common Arabic structure:

• قراءة الكتاب = reading the book
• زيارة المدينة = visiting the city
• فهم الدرس = understanding the lesson

It refers to the friend.

The clue is the feminine pronoun and adjective:

• ها in لأنها = she
• مريضة = feminine sick

So the meaning is:

• because she is sick

If it referred to we, the Arabic would look different:

• لأننا مرضى = because we are sick

Yes, in fully vocalized formal Arabic there would be case endings, but they are usually omitted in normal writing.

A fully vocalized version could be:

• نُرِيدُ زِيَارَةَ صَدِيقَتِي فِي الْمَسَاءِ لِأَنَّهَا مَرِيضَةٌ

For a learner, the important point is:

• normal Arabic writing usually leaves these short vowels off
• educated speakers still know the grammar behind them

Not necessarily. In MSA, صديقتي usually just means my female friend.

Context decides whether it means:

• female friend
• girlfriend

If the sentence simply says صديقتي, the safest basic meaning for learners is my female friend unless context suggests romance.