صحة صديقتي أفضل اليوم، لكنها لا تذهب إلى العمل.

In Arabic, the present-tense to be is usually omitted.

So Arabic says something like:

• صحة صديقتي أفضل اليوم
• literally: my friend's health better today

This is a normal nominal sentence in Arabic.

If you wanted was or will be, Arabic would usually add a form of كان:

• كانت صحة صديقتي أفضل أمس = My friend's health was better yesterday
• ستكون صحة صديقتي أفضل غدًا = My friend's health will be better tomorrow

This is an iḍāfa construction, often called a possessive construction.

It is built like this:

• صحة = health
• صديقتي = my friend (female)

Together:

• صحة صديقتي = the health of my friend = my friend's health

A few useful points:

• صديقة means female friend
• the ending -ي means my
• so صديقتي = my female friend

In an iḍāfa, the first noun usually does not take الـ here, even though the whole phrase can still be definite because the second noun is definite.

Because صحة is followed by another noun in an iḍāfa construction.

• By itself, صحة is usually pronounced ṣiḥḥa
• In صحة صديقتي, it is pronounced more like ṣiḥḥat ṣadīqatī

So the ة (taa marbuuṭa) often sounds like:

• -a / -ah when the word stands alone
• -t when the word is connected grammatically, especially in an iḍāfa

This is very common in Arabic.

Normally, adjectives in Arabic agree in gender with the noun they describe. But أفضل is a special kind of word: it is an elative form, often used for better / best.

When Arabic uses this comparative form, it is usually kept in the masculine singular form, even if the thing being talked about is feminine.

So you get:

• صحتها أفضل = Her health is better
• هذه السيارة أفضل = This car is better
• فاطمة أفضل في الرياضيات = Fatima is better at math

So here أفضل is completely normal.

It can mean either better or best, depending on context.

In this sentence, it means better.

Why?

Because the context is about today, so the sense is that her health has improved compared with some earlier time.

If Arabic wants to make the comparison explicit, it can add من:

• صحة صديقتي أفضل من أمس = My friend's health is better than yesterday

Without that, context does the work.

لكنها means but she.

It breaks down as:

• لكنّ = but / however
• ها = she / her here as an attached pronoun meaning she

So:

• لكنها لا تذهب إلى العمل = but she does not go to work

You may also see:

• ولكنها

This is basically و + لكنّ + ها, and it often also means but she. Both are common, though لكنها is a little shorter and simpler.

Because the subject is she, referring to my friend.

In the present tense:

• يذهب = he goes
• تذهب = she goes

So:

• هي تذهب = she goes
• هي لا تذهب = she does not go

Arabic often leaves the separate pronoun هي unstated because the verb already shows the person and gender.

In this sentence, the feminine reference is also clear from لكنها.

Because the Arabic present tense often covers both meanings that English separates into:

• simple present: she does not go
• present progressive: she is not going

Arabic does not always make that distinction.

So لا تذهب can mean:

• she doesn't go
• she isn't going

The context decides. Since the sentence includes اليوم (today), many learners will naturally understand it as something like:

• Her health is better today, but she isn't going to work

So the Arabic is broader than the English form.

إلى means to.

So:

• تذهب إلى العمل = she goes to work

As for العمل, it literally means the work, but Arabic often uses the definite article in places where English does not.

So Arabic says:

• إلى العمل = literally to the work
• natural English: to work

This is normal and idiomatic.

Compare:

• أذهب إلى المدرسة = I go to school
• أذهب إلى الجامعة = I go to الجامعة / university

Yes. Arabic word order is more flexible than English word order.

The sentence as written:

• صحة صديقتي أفضل اليوم

is perfectly normal.

But you could also see:

• اليوم صحة صديقتي أفضل
• صحة صديقتي اليوم أفضل

These all mean roughly the same thing, though the emphasis can shift slightly.

The written version you were given sounds natural and straightforward.

A fully vowelled version would be:

• صِحَّةُ صَدِيقَتِي أَفْضَلُ الْيَوْمَ، لَكِنَّهَا لَا تَذْهَبُ إِلَى الْعَمَلِ.

A few notes:

• صِحَّةُ is nominative because it is the subject of the nominal sentence
• صَدِيقَتِي means my friend
• أَفْضَلُ is the predicate
• الْيَوْمَ is in the accusative as an adverbial expression of time
• الْعَمَلِ is genitive after إلى

In everyday unvowelled Arabic, these endings are normally not written, which is why learners often need to infer them from grammar.

Because صديقة is the feminine form.

• صديق = male friend
• صديقة = female friend

Then add -ي for my:

• صديقي = my male friend
• صديقتي = my female friend

So the sentence clearly tells you that the friend is female, which is why the second clause uses feminine forms like لكنها and تذهب.