Di depan cermin, kakak perempuan saya menyentuh dagunya dan merapikan alisnya.

Because di here is a preposition, not a verb prefix. As a preposition, it is written separately:

• di depan = in front of
• di rumah = at home
• di meja = on the table

This is different from the passive prefix di-, which is attached to a verb:

• ditulis = written
• dibaca = read

So di depan cermin is correct because it is a location phrase: in front of the mirror.

Indonesian often puts a place phrase or time phrase at the beginning to set the scene. It is very natural.

So:

• Di depan cermin, kakak perempuan saya menyentuh dagunya...

means the same basic thing as:

• Kakak perempuan saya menyentuh dagunya ... di depan cermin.

Starting with Di depan cermin just gives the location first, like In front of the mirror, ...

Not exactly. It specifically means my older sister.

• kakak = older sibling
• perempuan = female
• saya = my

So kakak perempuan saya = my older sister.

If you wanted my younger sister, you would say:

• adik perempuan saya

Yes, you could say kakak saya. That means my older sibling and does not specify male or female.

Adding perempuan makes it explicit that the older sibling is female:

• kakak saya = my older sibling
• kakak perempuan saya = my older sister
• kakak laki-laki saya = my older brother

So perempuan is there for clarity.

Dagu means chin.

The ending -nya shows possession here, so:

• dagu = chin
• dagunya = his/her chin

In this sentence, it refers to the older sister’s chin, so dagunya means her chin.

Because Indonesian often marks possession by attaching -nya directly to the noun.

• dagunya = her chin
• alisnya = her eyebrow / her eyebrows

This is especially common with body parts and things closely associated with a person.

In this sentence, -nya refers back to kakak perempuan saya.

Menyentuh means to touch.

It is a transitive verb, so it takes its object directly:

• menyentuh dagunya = touch her chin

You do not need a preposition between the verb and the thing being touched.

Merapikan comes from rapi, which means neat or tidy.

So merapikan means:

• to make neat
• to tidy
• to groom
• to straighten up

In this sentence, merapikan alisnya means something like tidying/grooming her eyebrows.

Because Indonesian often does not mark plural unless it is necessary.

So alisnya can naturally mean:

• her eyebrow
• her eyebrows

The context tells you what is meant. In a grooming context, English would usually say eyebrows, but Indonesian often leaves it as alisnya.

If someone really wanted to emphasize plurality, they could say alis-alisnya, but that is usually unnecessary here.

Yes.

The subject is kakak perempuan saya, and it applies to both verbs:

• menyentuh
• merapikan

So the structure is:

• [Subject] menyentuh ... dan merapikan ...

This is very normal in Indonesian. You do not need to repeat the subject before the second verb.

Yes, but the meaning changes slightly.

• saudara perempuan saya = my sister / my female sibling
• kakak perempuan saya = my older sister

So saudara perempuan saya does not tell you whether she is older or younger. Kakak perempuan saya specifically tells you she is older.

Saya is the more neutral and polite word for I / my.

• saya = neutral, polite, standard
• aku = more informal, personal

So kakak perempuan saya sounds standard and natural in general Indonesian. If you used aku, it would sound more casual:

• kakak perempuanku

That is also possible, but it has a different tone.