صديقتي كانت مريضة هذا الأسبوع، لكنها اليوم أفضل وصحتها أفضل.

صديقتي means my female friend.

The base word is صديقة, which means female friend. The ending -ي is an attached pronoun meaning my.

So:

• صديقة = female friend
• صديقتي = my female friend

A useful detail: when a noun ends in ـة, that ending usually becomes ت before a suffix is added. So:

صديقة + ي → صديقتي

If you were talking about a male friend, you would say صديقي.

Because the subject, صديقتي, is feminine.

In Arabic, verbs and adjectives often agree with the noun they refer to in gender. Since the friend is female:

• كانت = she was
• مريضة = sick in the feminine form

If the friend were male, you would say:

• كان instead of كانت
• مريض instead of مريضة

So the feminine forms here are required by the subject.

Because Arabic uses كان to express was/were in the past.

In the present tense, Arabic usually does not use a word for is/am/are. But in the past, it does.

Compare:

• صديقتي مريضة = My friend is sick
• صديقتي كانت مريضة = My friend was sick

So كانت is what makes the sentence past tense.

لكنها means but she.

It is made up of:

• لكنّ = but / however
• ها = she / her

So لكنها = but she

After that, Arabic does not need a separate present-tense verb is. So:

• لكنها اليوم أفضل

literally comes out something like:

• but she today better

Natural English adds is, but Arabic does not need it here.

Because أسبوع is a masculine noun.

Arabic demonstratives must agree with the noun in gender, so:

• هذا = this, for masculine singular nouns
• هذه = this, for feminine singular nouns

Since أسبوع is masculine, the correct phrase is:

• هذا الأسبوع = this week

Because in standard Arabic, after هذا or هذه, the noun is normally definite.

So Arabic says:

• هذا الأسبوع = this week
• هذه المدينة = this city

This is different from English, where this week has no article. In Arabic, the noun after the demonstrative is usually definite, so الأسبوع takes الـ.

Because Arabic often uses time expressions directly, without a preposition.

So it is very normal to say:

• هذا الأسبوع = this week
• اليوم = today

These work like adverbs of time in the sentence.

So:

• كانت مريضة هذا الأسبوع = She was sick this week
• لكنها اليوم أفضل = But today she is better

You do not need في here.

Here it means better.

The form أفضل can mean either better or best, depending on context. In this sentence, it is clearly comparative:

• اليوم أفضل = today she is better

Arabic often leaves the second half of the comparison unstated. The meaning is understood from context: better than before, better than earlier this week, and so on.

If you want to state the comparison explicitly, you can use من:

• أفضل من قبل = better than before

Because the final ـة changes to ت when a suffix is attached.

The base word is:

• صحة = health

Add ها = her, and you get:

• صحتها = her health

So this follows the same pattern as صديقتي:

• صديقة → صديقتي
• صحة → صحتها

Yes, it is natural and grammatically fine.

The first أفضل describes the person:

• لكنها اليوم أفضل = But today she is better

The second أفضل describes her health:

• وصحتها أفضل = and her health is better

So the repetition is meaningful, not accidental.

In English, you might choose a less repetitive wording, such as and her health is better too or and her health has improved. But in Arabic, repeating أفضل like this is perfectly acceptable.

Yes. Arabic word order is flexible.

For example, both of these are possible:

• صديقتي كانت مريضة
• كانت صديقتي مريضة

Both mean essentially the same thing, but the emphasis shifts slightly.

Also, in the second part:

• لكنها اليوم أفضل
• لكنها أفضل اليوم

Both are possible. Changing the order can change which part sounds more emphasized, but the meaning stays very close.

Because most normal Arabic writing leaves them out.

In everyday printed Arabic, you usually see:

• كانت
• مريضة
• أفضل
• صحتها

without full vowel marks.

In a fully vocalized teaching text, some endings would be shown more clearly. For example, learners may see forms like:

• مريضةً
• أفضلُ

Native readers usually understand these forms from grammar and context, even when the short vowels are not written.