صديقتي ما زالت مريضة، ولذلك تضع منشفة باردة على وجهها.

The base word is صديقة meaning female friend. When you attach the possessive suffix -ي meaning my, the ة changes to ت before the suffix:

صديقة + ي → صديقتي

So صديقتي means my female friend.

A useful comparison:

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

Because it refers to a female friend. The ending ة is a very common feminine marker in Arabic nouns and adjectives.

So:

• صديق = male friend
• صديقة = female friend

Since the sentence is about a woman or girl, the feminine form is used.

ما زالت means is still or continues to be.

So:

صديقتي ما زالت مريضة
= My friend is still sick

This is a very common Arabic expression. It does not mean a simple negation here; together, ما زال functions as an idiomatic expression meaning to still be / to continue to be.

Because the subject is feminine singular: صديقتي.

Arabic verbs agree with their subject in gender, so the feminine singular form is used:

• ما زال = masculine singular
• ما زالت = feminine singular

Since my friend is female, ما زالت is correct.

That is a very common learner question. In Modern Standard Arabic, ما زال is often used with a past-form verb but gives a present meaning: still is / remains.

So although زالت looks like a past form, the whole expression ما زالت means something like she is still.

You can think of it as a fixed grammatical expression rather than translating each piece separately.

Because adjectives in Arabic must agree with the noun they describe.

Since صديقتي is feminine singular, the adjective must also be feminine singular:

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

So صديقتي ما زالت مريضة is grammatically matched.

Arabic does not have an independent word for a or an. Indefiniteness is usually shown simply by the lack of ال.

So:

• منشفة باردة = a cold towel
• المنشفة الباردة = the cold towel

This is one of the biggest differences from English.

Because in Arabic, descriptive adjectives normally come after the noun they describe.

So:

• منشفة باردة = a cold towel
• literally: towel cold

Also, the adjective must agree with the noun in:

• gender
• number
• definiteness
• case

Here both are feminine singular and indefinite:

• منشفة = towel
• باردة = cold

Because the subject is feminine singular.

In the present tense:

• يضع = he puts
• تضع = she puts

Since the sentence is about my female friend, Arabic uses تضع.

Because Arabic verbs already show person, number, and often gender.

So تضع already tells you she puts in this context. Arabic often drops subject pronouns when they are clear from the verb.

You could add هي for emphasis, but normally it is unnecessary:

• تضع منشفة باردة = She puts a cold towel
• هي تضع منشفة باردة = She is the one putting a cold towel / extra emphasis

ولذلك means and therefore, and for that reason, or simply so.

It is made of:

• و = and
• لذلك = for that reason / therefore

So the sentence structure is:

My friend is still sick, and therefore she puts a cold towel on her face.

You could also see just لذلك without و, depending on style.

Because على is the preposition meaning on.

So:

• على وجهها = on her face

And وجهها breaks down as:

• وجه = face
• ها = her

So وجهها means her face.

The suffix -ها means her.

So:

• وجه = face
• وجهها = her face

Arabic often expresses possession by attaching pronoun suffixes directly to nouns.

Other examples:

• وجهي = my face
• وجهك = your face
• وجهه = his face
• وجهها = her face

Yes. Arabic allows more than one word order.

Both of these are possible:

• صديقتي ما زالت مريضة
• ما زالت صديقتي مريضة

The version in your sentence starts with صديقتي, which makes my friend the topic. It feels a bit like setting up what the sentence is about first.

The other order can sound a bit more neutral or more verbal in flow.

Yes. لا تزال is a very common standard alternative and also means is still.

So:

• صديقتي ما زالت مريضة
• صديقتي لا تزال مريضة

Both can mean My friend is still sick.

For learners of Modern Standard Arabic, لا يزال / لا تزال is often taught as a very safe standard form.

Because normal Arabic writing usually leaves out short vowels and most case endings.

So in fully vocalized formal Arabic, you might see something like:

صديقتي ما زالت مريضةً، ولذلك تضعُ منشفةً باردةً على وجهِها.

But in ordinary writing, these endings are usually not written:

• مريضةً appears as مريضة
• منشفةً appears as منشفة
• وجهِها appears as وجهها

This is completely normal in everyday printed Arabic.