Η αδερφή μου έχει συνηθίσει να χρησιμοποιεί ενυδατική κρέμα μετά το ντους, αλλά εγώ το ξεχνάω συχνά.

In Greek, short possessive pronouns like μου often come after the noun:

• η αδερφή μου = my sister
• το σπίτι μου = my house

That is the normal everyday pattern. Greek does not usually say the equivalent of English my sister with the possessive first.

If you want extra emphasis, Greek can use δικός/δική/δικό:

• η δική μου αδερφή = my own sister / my sister (as opposed to someone else’s)

Yes, but the difference is mostly about style/register, not meaning.

• αδερφή is the very common everyday form.
• αδελφή is also correct, but sounds more formal, conservative, or old-fashioned to many speakers.

Both mean sister.

Yes, literally it is something like has gotten used to, but in natural English the idea is often simply is used to.

So:

• έχει συνηθίσει να χρησιμοποιεί...
  means she has become used to using..., and therefore now she is used to using...

Greek often uses this perfect form to describe a present state that resulted from past repetition or experience.

This is a very common learner question, because the two can look similar in translation.

• έχει συνηθίσει να... = is used to / has gotten used to
• συνηθίζει να... = usually does / tends to do / has the habit of doing

So:

• Η αδερφή μου έχει συνηθίσει να χρησιμοποιεί ενυδατική κρέμα...
  = she is accustomed to doing it

But:

• Η αδερφή μου συνηθίζει να χρησιμοποιεί ενυδατική κρέμα...
  = she habitually does it

The first emphasizes being accustomed; the second emphasizes regular behavior.

Because Modern Greek does not use the infinitive the way English does.

English says:

• to use

Modern Greek normally uses:

• να χρησιμοποιεί

This is να + a finite verb form, often called the subjunctive in learner materials.

So after verbs like συνηθίζω / έχω συνηθίσει, Greek says:

• έχει συνηθίσει να χρησιμοποιεί
• not an infinitive equivalent of to use

This is about aspect, which is very important in Greek.

After να, Greek often chooses between:

• imperfective: να χρησιμοποιεί
• perfective: να χρησιμοποιήσει

Here, να χρησιμοποιεί is used because the action is understood as repeated/habitual:

• using moisturizing cream after showers, as a routine

If you used να χρησιμοποιήσει, it would sound more like one complete act of using it, not a repeated habit.

So in this sentence, the imperfective form is the natural choice.

It is a noun phrase made of:

• ενυδατική = moisturizing / hydrating
• κρέμα = cream

So literally it is moisturizing cream.

The adjective ενυδατική agrees with κρέμα in gender, number, and case:

• κρέμα is feminine singular
• so the adjective is also feminine singular: ενυδατική

This is very normal Greek adjective agreement.

Greek often uses the definite article where English may or may not use one.

Here:

• μετά το ντους = after the shower / after showering

The noun ντους normally appears with the article here:

• το ντους

Also, in Modern Greek, μετά commonly takes the accusative:

• μετά το ντους

You may also hear:

• μετά από το ντους

Both are possible in everyday Greek.

ντους is a borrowed word, and it is typically treated as a neuter noun:

• το ντους

It is also usually indeclinable, meaning its form does not really change across cases the way many Greek nouns do.

So you get:

• το ντους
• μετά το ντους

without changing the noun itself.

Here το is a direct-object clitic pronoun meaning something like it.

But it does not refer to one single noun only. It refers to the whole idea/action just mentioned:

• using moisturizing cream after the shower

So:

• αλλά εγώ το ξεχνάω συχνά = but I often forget it / forget to do that

Greek very often uses το to refer back to a whole action, idea, or situation.

Yes. The verb ending already shows the subject:

• ξεχνάω = I forget

So εγώ is not required for basic grammar. It is used here for contrast/emphasis:

• but I often forget it

That contrasts the speaker with the sister:

• she is used to doing it, but I am not / I forget

This is a very common reason to include subject pronouns in Greek.

Yes. They are two common forms of the same verb:

• ξεχνάω
• ξεχνώ

Both mean I forget.

In everyday spoken Greek, forms in -άω are very common. You will often see both variants in dictionaries and real usage. The difference is mostly one of style and preference, not meaning.

Greek word order is fairly flexible, and adverbs like συχνά can move around.

In this sentence:

• αλλά εγώ το ξεχνάω συχνά

the end position sounds very natural.

You could also say:

• αλλά εγώ συχνά το ξεχνάω
• αλλά εγώ το συχνά ξεχνάω (much less natural here)

The version in the sentence is the most neutral and natural. Putting συχνά at the end gives a smooth everyday rhythm and lightly emphasizes the frequency.

Because Greek often leaves the subject implicit when it is already clear.

In:

• Η αδερφή μου έχει συνηθίσει να χρησιμοποιεί...

the subject of χρησιμοποιεί is understood to be the same as the subject of the main clause: η αδερφή μου.

So Greek does not need to repeat η αδερφή μου again.

English also often does something similar:

• My sister is used to using...

You do not repeat my sister before using either.